mm: frontswap: core frontswap functionality
This patch, 3of4, provides the core frontswap code that interfaces between the hooks in the swap subsystem and a frontswap backend via frontswap_ops. --- New file added: mm/frontswap.c [v14: add support for writethrough, per suggestion by aarcange@redhat.com] [v11: sjenning@linux.vnet.ibm.com: s/puts/failed_puts/] [v10: sjenning@linux.vnet.ibm.com: fix debugfs calls on 32-bit] [v9: akpm@linux-foundation.org: change "flush" to "invalidate", part 1] [v9: akpm@linux-foundation.org: mark some statics __read_mostly] [v9: akpm@linux-foundation.org: add clarifying comments] [v9: akpm@linux-foundation.org: no need to loop repeating try_to_unuse] [v9: error27@gmail.com: remove superfluous check for NULL] [v8: rebase to 3.0-rc4] [v8: kamezawa.hiroyu@jp.fujitsu.com: add comment to clarify find_next_to_unuse] [v7: rebase to 3.0-rc3] [v7: JBeulich@novell.com: use new static inlines, no-ops if not config'd] [v6: rebase to 3.1-rc1] [v6: lliubbo@gmail.com: use vzalloc] [v6: lliubbo@gmail.com: fix null pointer deref if vzalloc fails] [v6: konrad.wilk@oracl.com: various checks and code clarifications/comments] [v4: rebase to 2.6.39] Signed-off-by: Dan Magenheimer <dan.magenheimer@oracle.com> Acked-by: Jan Beulich <JBeulich@novell.com> Acked-by: Seth Jennings <sjenning@linux.vnet.ibm.com> Cc: Jeremy Fitzhardinge <jeremy@goop.org> Cc: Hugh Dickins <hughd@google.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Nitin Gupta <ngupta@vflare.org> Cc: Matthew Wilcox <matthew@wil.cx> Cc: Chris Mason <chris.mason@oracle.com> Cc: Rik Riel <riel@redhat.com> Cc: Andrew Morton <akpm@linux-foundation.org> [v12: Squashed s/flush/invalidate/ in] [v15: A bit of cleanup and seperate DEBUGFS] Signed-off-by: Konrad Wilk <konrad.wilk@oracle.com>
This commit is contained in:
Dan Magenheimer
Konrad Rzeszutek Wilk
parent
38b5faf4b1
commit
29f233cfff
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@ -0,0 +1,314 @@
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/*
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* Frontswap frontend
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*
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* This code provides the generic "frontend" layer to call a matching
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* "backend" driver implementation of frontswap. See
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* Documentation/vm/frontswap.txt for more information.
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*
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* Copyright (C) 2009-2012 Oracle Corp. All rights reserved.
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* Author: Dan Magenheimer
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*
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* This work is licensed under the terms of the GNU GPL, version 2.
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*/
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#include <linux/mm.h>
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#include <linux/mman.h>
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#include <linux/swap.h>
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#include <linux/swapops.h>
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#include <linux/proc_fs.h>
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#include <linux/security.h>
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#include <linux/capability.h>
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#include <linux/module.h>
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#include <linux/uaccess.h>
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#include <linux/debugfs.h>
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#include <linux/frontswap.h>
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#include <linux/swapfile.h>
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/*
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* frontswap_ops is set by frontswap_register_ops to contain the pointers
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* to the frontswap "backend" implementation functions.
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*/
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static struct frontswap_ops frontswap_ops __read_mostly;
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/*
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* This global enablement flag reduces overhead on systems where frontswap_ops
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* has not been registered, so is preferred to the slower alternative: a
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* function call that checks a non-global.
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*/
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bool frontswap_enabled __read_mostly;
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EXPORT_SYMBOL(frontswap_enabled);
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/*
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* If enabled, frontswap_put will return failure even on success. As
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* a result, the swap subsystem will always write the page to swap, in
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* effect converting frontswap into a writethrough cache. In this mode,
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* there is no direct reduction in swap writes, but a frontswap backend
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* can unilaterally "reclaim" any pages in use with no data loss, thus
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* providing increases control over maximum memory usage due to frontswap.
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*/
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static bool frontswap_writethrough_enabled __read_mostly;
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#ifdef CONFIG_DEBUG_FS
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/*
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* Counters available via /sys/kernel/debug/frontswap (if debugfs is
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* properly configured). These are for information only so are not protected
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* against increment races.
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*/
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static u64 frontswap_gets;
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static u64 frontswap_succ_puts;
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static u64 frontswap_failed_puts;
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static u64 frontswap_invalidates;
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static inline void inc_frontswap_gets(void) {
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frontswap_gets++;
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}
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static inline void inc_frontswap_succ_puts(void) {
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frontswap_succ_puts++;
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}
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static inline void inc_frontswap_failed_puts(void) {
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frontswap_failed_puts++;
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}
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static inline void inc_frontswap_invalidates(void) {
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frontswap_invalidates++;
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}
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#else
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static inline void inc_frontswap_gets(void) { }
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static inline void inc_frontswap_succ_puts(void) { }
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static inline void inc_frontswap_failed_puts(void) { }
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static inline void inc_frontswap_invalidates(void) { }
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#endif
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/*
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* Register operations for frontswap, returning previous thus allowing
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* detection of multiple backends and possible nesting.
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*/
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struct frontswap_ops frontswap_register_ops(struct frontswap_ops *ops)
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{
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struct frontswap_ops old = frontswap_ops;
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frontswap_ops = *ops;
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frontswap_enabled = true;
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return old;
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}
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EXPORT_SYMBOL(frontswap_register_ops);
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/*
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* Enable/disable frontswap writethrough (see above).
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*/
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void frontswap_writethrough(bool enable)
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{
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frontswap_writethrough_enabled = enable;
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}
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EXPORT_SYMBOL(frontswap_writethrough);
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/*
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* Called when a swap device is swapon'd.
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*/
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void __frontswap_init(unsigned type)
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{
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struct swap_info_struct *sis = swap_info[type];
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BUG_ON(sis == NULL);
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if (sis->frontswap_map == NULL)
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return;
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if (frontswap_enabled)
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(*frontswap_ops.init)(type);
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}
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EXPORT_SYMBOL(__frontswap_init);
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/*
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* "Put" data from a page to frontswap and associate it with the page's
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* swaptype and offset. Page must be locked and in the swap cache.
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* If frontswap already contains a page with matching swaptype and
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* offset, the frontswap implmentation may either overwrite the data and
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* return success or invalidate the page from frontswap and return failure.
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*/
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int __frontswap_put_page(struct page *page)
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{
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int ret = -1, dup = 0;
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swp_entry_t entry = { .val = page_private(page), };
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int type = swp_type(entry);
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struct swap_info_struct *sis = swap_info[type];
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pgoff_t offset = swp_offset(entry);
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BUG_ON(!PageLocked(page));
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BUG_ON(sis == NULL);
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if (frontswap_test(sis, offset))
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dup = 1;
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ret = (*frontswap_ops.put_page)(type, offset, page);
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if (ret == 0) {
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frontswap_set(sis, offset);
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inc_frontswap_succ_puts();
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if (!dup)
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atomic_inc(&sis->frontswap_pages);
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} else if (dup) {
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/*
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failed dup always results in automatic invalidate of
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the (older) page from frontswap
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*/
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frontswap_clear(sis, offset);
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atomic_dec(&sis->frontswap_pages);
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inc_frontswap_failed_puts();
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} else
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inc_frontswap_failed_puts();
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if (frontswap_writethrough_enabled)
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/* report failure so swap also writes to swap device */
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ret = -1;
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return ret;
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}
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EXPORT_SYMBOL(__frontswap_put_page);
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/*
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* "Get" data from frontswap associated with swaptype and offset that were
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* specified when the data was put to frontswap and use it to fill the
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* specified page with data. Page must be locked and in the swap cache.
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*/
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int __frontswap_get_page(struct page *page)
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{
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int ret = -1;
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swp_entry_t entry = { .val = page_private(page), };
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int type = swp_type(entry);
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struct swap_info_struct *sis = swap_info[type];
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pgoff_t offset = swp_offset(entry);
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BUG_ON(!PageLocked(page));
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BUG_ON(sis == NULL);
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if (frontswap_test(sis, offset))
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ret = (*frontswap_ops.get_page)(type, offset, page);
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if (ret == 0)
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inc_frontswap_gets();
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return ret;
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}
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EXPORT_SYMBOL(__frontswap_get_page);
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/*
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* Invalidate any data from frontswap associated with the specified swaptype
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* and offset so that a subsequent "get" will fail.
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*/
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void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
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{
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struct swap_info_struct *sis = swap_info[type];
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BUG_ON(sis == NULL);
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if (frontswap_test(sis, offset)) {
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(*frontswap_ops.invalidate_page)(type, offset);
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atomic_dec(&sis->frontswap_pages);
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frontswap_clear(sis, offset);
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inc_frontswap_invalidates();
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}
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}
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EXPORT_SYMBOL(__frontswap_invalidate_page);
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/*
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* Invalidate all data from frontswap associated with all offsets for the
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* specified swaptype.
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*/
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void __frontswap_invalidate_area(unsigned type)
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{
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struct swap_info_struct *sis = swap_info[type];
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BUG_ON(sis == NULL);
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if (sis->frontswap_map == NULL)
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return;
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(*frontswap_ops.invalidate_area)(type);
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atomic_set(&sis->frontswap_pages, 0);
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memset(sis->frontswap_map, 0, sis->max / sizeof(long));
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}
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EXPORT_SYMBOL(__frontswap_invalidate_area);
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/*
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* Frontswap, like a true swap device, may unnecessarily retain pages
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* under certain circumstances; "shrink" frontswap is essentially a
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* "partial swapoff" and works by calling try_to_unuse to attempt to
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* unuse enough frontswap pages to attempt to -- subject to memory
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* constraints -- reduce the number of pages in frontswap to the
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* number given in the parameter target_pages.
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*/
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void frontswap_shrink(unsigned long target_pages)
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{
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struct swap_info_struct *si = NULL;
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int si_frontswap_pages;
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unsigned long total_pages = 0, total_pages_to_unuse;
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unsigned long pages = 0, pages_to_unuse = 0;
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int type;
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bool locked = false;
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/*
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* we don't want to hold swap_lock while doing a very
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* lengthy try_to_unuse, but swap_list may change
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* so restart scan from swap_list.head each time
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*/
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spin_lock(&swap_lock);
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locked = true;
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total_pages = 0;
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for (type = swap_list.head; type >= 0; type = si->next) {
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si = swap_info[type];
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total_pages += atomic_read(&si->frontswap_pages);
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}
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if (total_pages <= target_pages)
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goto out;
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total_pages_to_unuse = total_pages - target_pages;
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for (type = swap_list.head; type >= 0; type = si->next) {
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si = swap_info[type];
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si_frontswap_pages = atomic_read(&si->frontswap_pages);
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if (total_pages_to_unuse < si_frontswap_pages)
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pages = pages_to_unuse = total_pages_to_unuse;
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else {
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pages = si_frontswap_pages;
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pages_to_unuse = 0; /* unuse all */
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}
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/* ensure there is enough RAM to fetch pages from frontswap */
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if (security_vm_enough_memory_mm(current->mm, pages))
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continue;
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vm_unacct_memory(pages);
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break;
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}
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if (type < 0)
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goto out;
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locked = false;
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spin_unlock(&swap_lock);
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try_to_unuse(type, true, pages_to_unuse);
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out:
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if (locked)
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spin_unlock(&swap_lock);
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return;
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}
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EXPORT_SYMBOL(frontswap_shrink);
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/*
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* Count and return the number of frontswap pages across all
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* swap devices. This is exported so that backend drivers can
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* determine current usage without reading debugfs.
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*/
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unsigned long frontswap_curr_pages(void)
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{
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int type;
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unsigned long totalpages = 0;
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struct swap_info_struct *si = NULL;
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spin_lock(&swap_lock);
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for (type = swap_list.head; type >= 0; type = si->next) {
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si = swap_info[type];
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totalpages += atomic_read(&si->frontswap_pages);
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}
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spin_unlock(&swap_lock);
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return totalpages;
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}
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EXPORT_SYMBOL(frontswap_curr_pages);
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static int __init init_frontswap(void)
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{
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#ifdef CONFIG_DEBUG_FS
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struct dentry *root = debugfs_create_dir("frontswap", NULL);
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if (root == NULL)
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return -ENXIO;
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debugfs_create_u64("gets", S_IRUGO, root, &frontswap_gets);
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debugfs_create_u64("succ_puts", S_IRUGO, root, &frontswap_succ_puts);
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debugfs_create_u64("failed_puts", S_IRUGO, root,
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&frontswap_failed_puts);
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debugfs_create_u64("invalidates", S_IRUGO,
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root, &frontswap_invalidates);
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#endif
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return 0;
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}
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module_init(init_frontswap);
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