684 lines
17 KiB
C
684 lines
17 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* background writeback - scan btree for dirty data and write it to the backing
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* device
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*
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* Copyright 2010, 2011 Kent Overstreet <kent.overstreet@gmail.com>
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* Copyright 2012 Google, Inc.
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*/
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#include "bcache.h"
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#include "btree.h"
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#include "debug.h"
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#include "writeback.h"
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#include <linux/delay.h>
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#include <linux/kthread.h>
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#include <linux/sched/clock.h>
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#include <trace/events/bcache.h>
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/* Rate limiting */
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static uint64_t __calc_target_rate(struct cached_dev *dc)
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{
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struct cache_set *c = dc->disk.c;
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/*
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* This is the size of the cache, minus the amount used for
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* flash-only devices
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*/
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uint64_t cache_sectors = c->nbuckets * c->sb.bucket_size -
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bcache_flash_devs_sectors_dirty(c);
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/*
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* Unfortunately there is no control of global dirty data. If the
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* user states that they want 10% dirty data in the cache, and has,
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* e.g., 5 backing volumes of equal size, we try and ensure each
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* backing volume uses about 2% of the cache for dirty data.
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*/
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uint32_t bdev_share =
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div64_u64(bdev_sectors(dc->bdev) << WRITEBACK_SHARE_SHIFT,
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c->cached_dev_sectors);
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uint64_t cache_dirty_target =
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div_u64(cache_sectors * dc->writeback_percent, 100);
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/* Ensure each backing dev gets at least one dirty share */
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if (bdev_share < 1)
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bdev_share = 1;
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return (cache_dirty_target * bdev_share) >> WRITEBACK_SHARE_SHIFT;
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}
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static void __update_writeback_rate(struct cached_dev *dc)
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{
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/*
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* PI controller:
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* Figures out the amount that should be written per second.
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*
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* First, the error (number of sectors that are dirty beyond our
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* target) is calculated. The error is accumulated (numerically
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* integrated).
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*
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* Then, the proportional value and integral value are scaled
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* based on configured values. These are stored as inverses to
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* avoid fixed point math and to make configuration easy-- e.g.
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* the default value of 40 for writeback_rate_p_term_inverse
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* attempts to write at a rate that would retire all the dirty
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* blocks in 40 seconds.
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*
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* The writeback_rate_i_inverse value of 10000 means that 1/10000th
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* of the error is accumulated in the integral term per second.
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* This acts as a slow, long-term average that is not subject to
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* variations in usage like the p term.
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*/
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int64_t target = __calc_target_rate(dc);
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int64_t dirty = bcache_dev_sectors_dirty(&dc->disk);
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int64_t error = dirty - target;
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int64_t proportional_scaled =
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div_s64(error, dc->writeback_rate_p_term_inverse);
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int64_t integral_scaled;
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uint32_t new_rate;
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if ((error < 0 && dc->writeback_rate_integral > 0) ||
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(error > 0 && time_before64(local_clock(),
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dc->writeback_rate.next + NSEC_PER_MSEC))) {
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/*
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* Only decrease the integral term if it's more than
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* zero. Only increase the integral term if the device
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* is keeping up. (Don't wind up the integral
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* ineffectively in either case).
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*
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* It's necessary to scale this by
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* writeback_rate_update_seconds to keep the integral
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* term dimensioned properly.
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*/
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dc->writeback_rate_integral += error *
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dc->writeback_rate_update_seconds;
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}
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integral_scaled = div_s64(dc->writeback_rate_integral,
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dc->writeback_rate_i_term_inverse);
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new_rate = clamp_t(int32_t, (proportional_scaled + integral_scaled),
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dc->writeback_rate_minimum, NSEC_PER_SEC);
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dc->writeback_rate_proportional = proportional_scaled;
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dc->writeback_rate_integral_scaled = integral_scaled;
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dc->writeback_rate_change = new_rate - dc->writeback_rate.rate;
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dc->writeback_rate.rate = new_rate;
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dc->writeback_rate_target = target;
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}
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static void update_writeback_rate(struct work_struct *work)
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{
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struct cached_dev *dc = container_of(to_delayed_work(work),
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struct cached_dev,
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writeback_rate_update);
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down_read(&dc->writeback_lock);
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if (atomic_read(&dc->has_dirty) &&
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dc->writeback_percent)
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__update_writeback_rate(dc);
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up_read(&dc->writeback_lock);
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schedule_delayed_work(&dc->writeback_rate_update,
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dc->writeback_rate_update_seconds * HZ);
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}
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static unsigned writeback_delay(struct cached_dev *dc, unsigned sectors)
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{
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if (test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags) ||
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!dc->writeback_percent)
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return 0;
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return bch_next_delay(&dc->writeback_rate, sectors);
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}
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struct dirty_io {
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struct closure cl;
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struct cached_dev *dc;
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uint16_t sequence;
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struct bio bio;
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};
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static void dirty_init(struct keybuf_key *w)
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{
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struct dirty_io *io = w->private;
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struct bio *bio = &io->bio;
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bio_init(bio, bio->bi_inline_vecs,
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DIV_ROUND_UP(KEY_SIZE(&w->key), PAGE_SECTORS));
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if (!io->dc->writeback_percent)
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bio_set_prio(bio, IOPRIO_PRIO_VALUE(IOPRIO_CLASS_IDLE, 0));
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bio->bi_iter.bi_size = KEY_SIZE(&w->key) << 9;
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bio->bi_private = w;
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bch_bio_map(bio, NULL);
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}
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static void dirty_io_destructor(struct closure *cl)
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{
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struct dirty_io *io = container_of(cl, struct dirty_io, cl);
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kfree(io);
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}
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static void write_dirty_finish(struct closure *cl)
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{
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struct dirty_io *io = container_of(cl, struct dirty_io, cl);
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struct keybuf_key *w = io->bio.bi_private;
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struct cached_dev *dc = io->dc;
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bio_free_pages(&io->bio);
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/* This is kind of a dumb way of signalling errors. */
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if (KEY_DIRTY(&w->key)) {
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int ret;
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unsigned i;
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struct keylist keys;
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bch_keylist_init(&keys);
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bkey_copy(keys.top, &w->key);
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SET_KEY_DIRTY(keys.top, false);
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bch_keylist_push(&keys);
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for (i = 0; i < KEY_PTRS(&w->key); i++)
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atomic_inc(&PTR_BUCKET(dc->disk.c, &w->key, i)->pin);
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ret = bch_btree_insert(dc->disk.c, &keys, NULL, &w->key);
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if (ret)
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trace_bcache_writeback_collision(&w->key);
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atomic_long_inc(ret
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? &dc->disk.c->writeback_keys_failed
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: &dc->disk.c->writeback_keys_done);
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}
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bch_keybuf_del(&dc->writeback_keys, w);
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up(&dc->in_flight);
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closure_return_with_destructor(cl, dirty_io_destructor);
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}
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static void dirty_endio(struct bio *bio)
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{
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struct keybuf_key *w = bio->bi_private;
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struct dirty_io *io = w->private;
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if (bio->bi_status)
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SET_KEY_DIRTY(&w->key, false);
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closure_put(&io->cl);
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}
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static void write_dirty(struct closure *cl)
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{
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struct dirty_io *io = container_of(cl, struct dirty_io, cl);
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struct keybuf_key *w = io->bio.bi_private;
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struct cached_dev *dc = io->dc;
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uint16_t next_sequence;
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if (atomic_read(&dc->writeback_sequence_next) != io->sequence) {
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/* Not our turn to write; wait for a write to complete */
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closure_wait(&dc->writeback_ordering_wait, cl);
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if (atomic_read(&dc->writeback_sequence_next) == io->sequence) {
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/*
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* Edge case-- it happened in indeterminate order
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* relative to when we were added to wait list..
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*/
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closure_wake_up(&dc->writeback_ordering_wait);
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}
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continue_at(cl, write_dirty, io->dc->writeback_write_wq);
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return;
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}
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next_sequence = io->sequence + 1;
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/*
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* IO errors are signalled using the dirty bit on the key.
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* If we failed to read, we should not attempt to write to the
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* backing device. Instead, immediately go to write_dirty_finish
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* to clean up.
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*/
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if (KEY_DIRTY(&w->key)) {
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dirty_init(w);
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bio_set_op_attrs(&io->bio, REQ_OP_WRITE, 0);
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io->bio.bi_iter.bi_sector = KEY_START(&w->key);
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bio_set_dev(&io->bio, io->dc->bdev);
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io->bio.bi_end_io = dirty_endio;
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closure_bio_submit(&io->bio, cl);
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}
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atomic_set(&dc->writeback_sequence_next, next_sequence);
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closure_wake_up(&dc->writeback_ordering_wait);
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continue_at(cl, write_dirty_finish, io->dc->writeback_write_wq);
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}
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static void read_dirty_endio(struct bio *bio)
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{
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struct keybuf_key *w = bio->bi_private;
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struct dirty_io *io = w->private;
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/* is_read = 1 */
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bch_count_io_errors(PTR_CACHE(io->dc->disk.c, &w->key, 0),
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bio->bi_status, 1,
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"reading dirty data from cache");
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dirty_endio(bio);
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}
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static void read_dirty_submit(struct closure *cl)
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{
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struct dirty_io *io = container_of(cl, struct dirty_io, cl);
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closure_bio_submit(&io->bio, cl);
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continue_at(cl, write_dirty, io->dc->writeback_write_wq);
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}
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static void read_dirty(struct cached_dev *dc)
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{
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unsigned delay = 0;
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struct keybuf_key *next, *keys[MAX_WRITEBACKS_IN_PASS], *w;
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size_t size;
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int nk, i;
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struct dirty_io *io;
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struct closure cl;
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uint16_t sequence = 0;
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BUG_ON(!llist_empty(&dc->writeback_ordering_wait.list));
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atomic_set(&dc->writeback_sequence_next, sequence);
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closure_init_stack(&cl);
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/*
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* XXX: if we error, background writeback just spins. Should use some
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* mempools.
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*/
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next = bch_keybuf_next(&dc->writeback_keys);
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while (!kthread_should_stop() && next) {
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size = 0;
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nk = 0;
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do {
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BUG_ON(ptr_stale(dc->disk.c, &next->key, 0));
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/*
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* Don't combine too many operations, even if they
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* are all small.
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*/
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if (nk >= MAX_WRITEBACKS_IN_PASS)
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break;
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/*
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* If the current operation is very large, don't
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* further combine operations.
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*/
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if (size >= MAX_WRITESIZE_IN_PASS)
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break;
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/*
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* Operations are only eligible to be combined
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* if they are contiguous.
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*
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* TODO: add a heuristic willing to fire a
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* certain amount of non-contiguous IO per pass,
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* so that we can benefit from backing device
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* command queueing.
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*/
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if ((nk != 0) && bkey_cmp(&keys[nk-1]->key,
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&START_KEY(&next->key)))
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break;
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size += KEY_SIZE(&next->key);
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keys[nk++] = next;
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} while ((next = bch_keybuf_next(&dc->writeback_keys)));
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/* Now we have gathered a set of 1..5 keys to write back. */
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for (i = 0; i < nk; i++) {
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w = keys[i];
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io = kzalloc(sizeof(struct dirty_io) +
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sizeof(struct bio_vec) *
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DIV_ROUND_UP(KEY_SIZE(&w->key), PAGE_SECTORS),
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GFP_KERNEL);
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if (!io)
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goto err;
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w->private = io;
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io->dc = dc;
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io->sequence = sequence++;
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dirty_init(w);
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bio_set_op_attrs(&io->bio, REQ_OP_READ, 0);
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io->bio.bi_iter.bi_sector = PTR_OFFSET(&w->key, 0);
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bio_set_dev(&io->bio,
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PTR_CACHE(dc->disk.c, &w->key, 0)->bdev);
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io->bio.bi_end_io = read_dirty_endio;
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if (bch_bio_alloc_pages(&io->bio, GFP_KERNEL))
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goto err_free;
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trace_bcache_writeback(&w->key);
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down(&dc->in_flight);
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/* We've acquired a semaphore for the maximum
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* simultaneous number of writebacks; from here
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* everything happens asynchronously.
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*/
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closure_call(&io->cl, read_dirty_submit, NULL, &cl);
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}
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delay = writeback_delay(dc, size);
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/* If the control system would wait for at least half a
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* second, and there's been no reqs hitting the backing disk
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* for awhile: use an alternate mode where we have at most
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* one contiguous set of writebacks in flight at a time. If
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* someone wants to do IO it will be quick, as it will only
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* have to contend with one operation in flight, and we'll
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* be round-tripping data to the backing disk as quickly as
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* it can accept it.
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*/
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if (delay >= HZ / 2) {
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/* 3 means at least 1.5 seconds, up to 7.5 if we
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* have slowed way down.
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*/
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if (atomic_inc_return(&dc->backing_idle) >= 3) {
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/* Wait for current I/Os to finish */
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closure_sync(&cl);
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/* And immediately launch a new set. */
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delay = 0;
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}
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}
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while (!kthread_should_stop() && delay) {
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schedule_timeout_interruptible(delay);
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delay = writeback_delay(dc, 0);
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}
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}
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if (0) {
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err_free:
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kfree(w->private);
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err:
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bch_keybuf_del(&dc->writeback_keys, w);
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}
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/*
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* Wait for outstanding writeback IOs to finish (and keybuf slots to be
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* freed) before refilling again
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*/
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closure_sync(&cl);
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}
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/* Scan for dirty data */
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void bcache_dev_sectors_dirty_add(struct cache_set *c, unsigned inode,
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uint64_t offset, int nr_sectors)
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{
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struct bcache_device *d = c->devices[inode];
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unsigned stripe_offset, stripe, sectors_dirty;
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if (!d)
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return;
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stripe = offset_to_stripe(d, offset);
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stripe_offset = offset & (d->stripe_size - 1);
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while (nr_sectors) {
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int s = min_t(unsigned, abs(nr_sectors),
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d->stripe_size - stripe_offset);
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if (nr_sectors < 0)
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s = -s;
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if (stripe >= d->nr_stripes)
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return;
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sectors_dirty = atomic_add_return(s,
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d->stripe_sectors_dirty + stripe);
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if (sectors_dirty == d->stripe_size)
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set_bit(stripe, d->full_dirty_stripes);
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else
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clear_bit(stripe, d->full_dirty_stripes);
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nr_sectors -= s;
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stripe_offset = 0;
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stripe++;
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}
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}
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static bool dirty_pred(struct keybuf *buf, struct bkey *k)
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{
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struct cached_dev *dc = container_of(buf, struct cached_dev, writeback_keys);
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BUG_ON(KEY_INODE(k) != dc->disk.id);
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return KEY_DIRTY(k);
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}
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static void refill_full_stripes(struct cached_dev *dc)
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{
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struct keybuf *buf = &dc->writeback_keys;
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unsigned start_stripe, stripe, next_stripe;
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bool wrapped = false;
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stripe = offset_to_stripe(&dc->disk, KEY_OFFSET(&buf->last_scanned));
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if (stripe >= dc->disk.nr_stripes)
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stripe = 0;
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start_stripe = stripe;
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while (1) {
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stripe = find_next_bit(dc->disk.full_dirty_stripes,
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dc->disk.nr_stripes, stripe);
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if (stripe == dc->disk.nr_stripes)
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goto next;
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next_stripe = find_next_zero_bit(dc->disk.full_dirty_stripes,
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dc->disk.nr_stripes, stripe);
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buf->last_scanned = KEY(dc->disk.id,
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stripe * dc->disk.stripe_size, 0);
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bch_refill_keybuf(dc->disk.c, buf,
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&KEY(dc->disk.id,
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next_stripe * dc->disk.stripe_size, 0),
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dirty_pred);
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if (array_freelist_empty(&buf->freelist))
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return;
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stripe = next_stripe;
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next:
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if (wrapped && stripe > start_stripe)
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return;
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if (stripe == dc->disk.nr_stripes) {
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stripe = 0;
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wrapped = true;
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}
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}
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}
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/*
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* Returns true if we scanned the entire disk
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*/
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static bool refill_dirty(struct cached_dev *dc)
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{
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struct keybuf *buf = &dc->writeback_keys;
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struct bkey start = KEY(dc->disk.id, 0, 0);
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struct bkey end = KEY(dc->disk.id, MAX_KEY_OFFSET, 0);
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struct bkey start_pos;
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/*
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|
* make sure keybuf pos is inside the range for this disk - at bringup
|
|
* we might not be attached yet so this disk's inode nr isn't
|
|
* initialized then
|
|
*/
|
|
if (bkey_cmp(&buf->last_scanned, &start) < 0 ||
|
|
bkey_cmp(&buf->last_scanned, &end) > 0)
|
|
buf->last_scanned = start;
|
|
|
|
if (dc->partial_stripes_expensive) {
|
|
refill_full_stripes(dc);
|
|
if (array_freelist_empty(&buf->freelist))
|
|
return false;
|
|
}
|
|
|
|
start_pos = buf->last_scanned;
|
|
bch_refill_keybuf(dc->disk.c, buf, &end, dirty_pred);
|
|
|
|
if (bkey_cmp(&buf->last_scanned, &end) < 0)
|
|
return false;
|
|
|
|
/*
|
|
* If we get to the end start scanning again from the beginning, and
|
|
* only scan up to where we initially started scanning from:
|
|
*/
|
|
buf->last_scanned = start;
|
|
bch_refill_keybuf(dc->disk.c, buf, &start_pos, dirty_pred);
|
|
|
|
return bkey_cmp(&buf->last_scanned, &start_pos) >= 0;
|
|
}
|
|
|
|
static int bch_writeback_thread(void *arg)
|
|
{
|
|
struct cached_dev *dc = arg;
|
|
bool searched_full_index;
|
|
|
|
bch_ratelimit_reset(&dc->writeback_rate);
|
|
|
|
while (!kthread_should_stop()) {
|
|
down_write(&dc->writeback_lock);
|
|
set_current_state(TASK_INTERRUPTIBLE);
|
|
if (!atomic_read(&dc->has_dirty) ||
|
|
(!test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags) &&
|
|
!dc->writeback_running)) {
|
|
up_write(&dc->writeback_lock);
|
|
|
|
if (kthread_should_stop()) {
|
|
set_current_state(TASK_RUNNING);
|
|
return 0;
|
|
}
|
|
|
|
schedule();
|
|
continue;
|
|
}
|
|
set_current_state(TASK_RUNNING);
|
|
|
|
searched_full_index = refill_dirty(dc);
|
|
|
|
if (searched_full_index &&
|
|
RB_EMPTY_ROOT(&dc->writeback_keys.keys)) {
|
|
atomic_set(&dc->has_dirty, 0);
|
|
cached_dev_put(dc);
|
|
SET_BDEV_STATE(&dc->sb, BDEV_STATE_CLEAN);
|
|
bch_write_bdev_super(dc, NULL);
|
|
}
|
|
|
|
up_write(&dc->writeback_lock);
|
|
|
|
read_dirty(dc);
|
|
|
|
if (searched_full_index) {
|
|
unsigned delay = dc->writeback_delay * HZ;
|
|
|
|
while (delay &&
|
|
!kthread_should_stop() &&
|
|
!test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags))
|
|
delay = schedule_timeout_interruptible(delay);
|
|
|
|
bch_ratelimit_reset(&dc->writeback_rate);
|
|
}
|
|
}
|
|
|
|
return 0;
|
|
}
|
|
|
|
/* Init */
|
|
|
|
struct sectors_dirty_init {
|
|
struct btree_op op;
|
|
unsigned inode;
|
|
};
|
|
|
|
static int sectors_dirty_init_fn(struct btree_op *_op, struct btree *b,
|
|
struct bkey *k)
|
|
{
|
|
struct sectors_dirty_init *op = container_of(_op,
|
|
struct sectors_dirty_init, op);
|
|
if (KEY_INODE(k) > op->inode)
|
|
return MAP_DONE;
|
|
|
|
if (KEY_DIRTY(k))
|
|
bcache_dev_sectors_dirty_add(b->c, KEY_INODE(k),
|
|
KEY_START(k), KEY_SIZE(k));
|
|
|
|
return MAP_CONTINUE;
|
|
}
|
|
|
|
void bch_sectors_dirty_init(struct bcache_device *d)
|
|
{
|
|
struct sectors_dirty_init op;
|
|
|
|
bch_btree_op_init(&op.op, -1);
|
|
op.inode = d->id;
|
|
|
|
bch_btree_map_keys(&op.op, d->c, &KEY(op.inode, 0, 0),
|
|
sectors_dirty_init_fn, 0);
|
|
}
|
|
|
|
void bch_cached_dev_writeback_init(struct cached_dev *dc)
|
|
{
|
|
sema_init(&dc->in_flight, 64);
|
|
init_rwsem(&dc->writeback_lock);
|
|
bch_keybuf_init(&dc->writeback_keys);
|
|
|
|
dc->writeback_metadata = true;
|
|
dc->writeback_running = true;
|
|
dc->writeback_percent = 10;
|
|
dc->writeback_delay = 30;
|
|
dc->writeback_rate.rate = 1024;
|
|
dc->writeback_rate_minimum = 8;
|
|
|
|
dc->writeback_rate_update_seconds = WRITEBACK_RATE_UPDATE_SECS_DEFAULT;
|
|
dc->writeback_rate_p_term_inverse = 40;
|
|
dc->writeback_rate_i_term_inverse = 10000;
|
|
|
|
INIT_DELAYED_WORK(&dc->writeback_rate_update, update_writeback_rate);
|
|
}
|
|
|
|
int bch_cached_dev_writeback_start(struct cached_dev *dc)
|
|
{
|
|
dc->writeback_write_wq = alloc_workqueue("bcache_writeback_wq",
|
|
WQ_MEM_RECLAIM, 0);
|
|
if (!dc->writeback_write_wq)
|
|
return -ENOMEM;
|
|
|
|
dc->writeback_thread = kthread_create(bch_writeback_thread, dc,
|
|
"bcache_writeback");
|
|
if (IS_ERR(dc->writeback_thread))
|
|
return PTR_ERR(dc->writeback_thread);
|
|
|
|
schedule_delayed_work(&dc->writeback_rate_update,
|
|
dc->writeback_rate_update_seconds * HZ);
|
|
|
|
bch_writeback_queue(dc);
|
|
|
|
return 0;
|
|
}
|