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writeback, memcg: Implement cgroup_writeback_by_id() 

Implement cgroup_writeback_by_id() which initiates cgroup writeback
from bdi and memcg IDs.  This will be used by memcg foreign inode
flushing.

v2: Use wb_get_lookup() instead of wb_get_create() to avoid creating
    spurious wbs.

v3: Interpret 0 @nr as 1.25 * nr_dirty to implement best-effort
    flushing while avoding possible livelocks.

Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Tejun Heo 2019-08-26 09:06:55 -07:00 committed by Jens Axboe
parent ed288dc0d4
commit d62241c7a4
2 changed files with 85 additions and 0 deletions
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83
fs/fs-writeback.c
View File

@ -891,6 +891,89 @@ restart:
wb_put(last_wb);
}
/**
* cgroup_writeback_by_id - initiate cgroup writeback from bdi and memcg IDs
* @bdi_id: target bdi id
* @memcg_id: target memcg css id
* @nr_pages: number of pages to write, 0 for best-effort dirty flushing
* @reason: reason why some writeback work initiated
* @done: target wb_completion
*
* Initiate flush of the bdi_writeback identified by @bdi_id and @memcg_id
* with the specified parameters.
*/
int cgroup_writeback_by_id(u64 bdi_id, int memcg_id, unsigned long nr,
enum wb_reason reason, struct wb_completion *done)
{
struct backing_dev_info *bdi;
struct cgroup_subsys_state *memcg_css;
struct bdi_writeback *wb;
struct wb_writeback_work *work;
int ret;
/* lookup bdi and memcg */
bdi = bdi_get_by_id(bdi_id);
if (!bdi)
return -ENOENT;
rcu_read_lock();
memcg_css = css_from_id(memcg_id, &memory_cgrp_subsys);
if (memcg_css && !css_tryget(memcg_css))
memcg_css = NULL;
rcu_read_unlock();
if (!memcg_css) {
ret = -ENOENT;
goto out_bdi_put;
}
/*
* And find the associated wb. If the wb isn't there already
* there's nothing to flush, don't create one.
*/
wb = wb_get_lookup(bdi, memcg_css);
if (!wb) {
ret = -ENOENT;
goto out_css_put;
}
/*
* If @nr is zero, the caller is attempting to write out most of
* the currently dirty pages. Let's take the current dirty page
* count and inflate it by 25% which should be large enough to
* flush out most dirty pages while avoiding getting livelocked by
* concurrent dirtiers.
*/
if (!nr) {
unsigned long filepages, headroom, dirty, writeback;
mem_cgroup_wb_stats(wb, &filepages, &headroom, &dirty,
&writeback);
nr = dirty * 10 / 8;
}
/* issue the writeback work */
work = kzalloc(sizeof(*work), GFP_NOWAIT | __GFP_NOWARN);
if (work) {
work->nr_pages = nr;
work->sync_mode = WB_SYNC_NONE;
work->range_cyclic = 1;
work->reason = reason;
work->done = done;
work->auto_free = 1;
wb_queue_work(wb, work);
ret = 0;
} else {
ret = -ENOMEM;
}
wb_put(wb);
out_css_put:
css_put(memcg_css);
out_bdi_put:
bdi_put(bdi);
return ret;
}
/**
* cgroup_writeback_umount - flush inode wb switches for umount
*

2
include/linux/writeback.h
View File

@ -217,6 +217,8 @@ void wbc_attach_and_unlock_inode(struct writeback_control *wbc,
void wbc_detach_inode(struct writeback_control *wbc);
void wbc_account_cgroup_owner(struct writeback_control *wbc, struct page *page,
size_t bytes);
int cgroup_writeback_by_id(u64 bdi_id, int memcg_id, unsigned long nr_pages,
enum wb_reason reason, struct wb_completion *done);
void cgroup_writeback_umount(void);
/**