Commit 11f81bec authored by Tejun Heo's avatar Tejun Heo Committed by Jens Axboe
Browse files

page_writeback: revive cancel_dirty_page() in a restricted form 



cancel_dirty_page() had some issues and b9ea2515 ("page_writeback:
clean up mess around cancel_dirty_page()") replaced it with
account_page_cleaned() which makes the caller responsible for clearing
the dirty bit; unfortunately, the planned changes for cgroup writeback
support requires synchronization between dirty bit manipulation and
stat updates.  While we can open-code such synchronization in each
account_page_cleaned() callsite, that's gonna be unnecessarily awkward
and verbose.

This patch revives cancel_dirty_page() but in a more restricted form.
All it does is TestClearPageDirty() followed by account_page_cleaned()
invocation if the page was dirty.  This helper covers all
account_page_cleaned() usages except for __delete_from_page_cache()
which is a special case anyway and left alone.  As this leaves no
module user for account_page_cleaned(), EXPORT_SYMBOL() is dropped
from it.

This patch just revives cancel_dirty_page() as a trivial wrapper to
replace equivalent usages and doesn't introduce any functional
changes.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
parent f26cdc85

drivers/staging/lustre/lustre/include/linux/lustre_patchless_compat.h

+1 −3
Original line number Diff line number Diff line
@@ -55,9 +55,7 @@ truncate_complete_page(struct address_space *mapping, struct page *page) 
	if (PagePrivate(page))

		page->mapping->a_ops->invalidatepage(page, 0, PAGE_CACHE_SIZE);



	if (TestClearPageDirty(page))

		account_page_cleaned(page, mapping);



	cancel_dirty_page(page);

	ClearPageMappedToDisk(page);

	ll_delete_from_page_cache(page);

}

fs/buffer.c

+2 −2
Original line number Diff line number Diff line
@@ -3232,8 +3232,8 @@ int try_to_free_buffers(struct page *page) 
	 * to synchronise against __set_page_dirty_buffers and prevent the

	 * dirty bit from being lost.

	 */

	if (ret && TestClearPageDirty(page))

		account_page_cleaned(page, mapping);

	if (ret)

		cancel_dirty_page(page);

	spin_unlock(&mapping->private_lock);

out:

	if (buffers_to_free) {

include/linux/mm.h

+1 −0
Original line number Diff line number Diff line
@@ -1215,6 +1215,7 @@ void account_page_dirtied(struct page *page, struct address_space *mapping); 
void account_page_cleaned(struct page *page, struct address_space *mapping);

int set_page_dirty(struct page *page);

int set_page_dirty_lock(struct page *page);

void cancel_dirty_page(struct page *page);

int clear_page_dirty_for_io(struct page *page);



int get_cmdline(struct task_struct *task, char *buffer, int buflen);

mm/page-writeback.c

+20 −7
Original line number Diff line number Diff line
@@ -2112,12 +2112,6 @@ EXPORT_SYMBOL(account_page_dirtied); 


/*

 * Helper function for deaccounting dirty page without writeback.

 *

 * Doing this should *normally* only ever be done when a page

 * is truncated, and is not actually mapped anywhere at all. However,

 * fs/buffer.c does this when it notices that somebody has cleaned

 * out all the buffers on a page without actually doing it through

 * the VM. Can you say "ext3 is horribly ugly"? Thought you could.

 */

void account_page_cleaned(struct page *page, struct address_space *mapping)

{
@@ -2127,7 +2121,6 @@ void account_page_cleaned(struct page *page, struct address_space *mapping) 
		task_io_account_cancelled_write(PAGE_CACHE_SIZE);

	}

}

EXPORT_SYMBOL(account_page_cleaned);



/*

 * For address_spaces which do not use buffers.  Just tag the page as dirty in
@@ -2265,6 +2258,26 @@ int set_page_dirty_lock(struct page *page) 
}

EXPORT_SYMBOL(set_page_dirty_lock);



/*

 * This cancels just the dirty bit on the kernel page itself, it does NOT

 * actually remove dirty bits on any mmap's that may be around. It also

 * leaves the page tagged dirty, so any sync activity will still find it on

 * the dirty lists, and in particular, clear_page_dirty_for_io() will still

 * look at the dirty bits in the VM.

 *

 * Doing this should *normally* only ever be done when a page is truncated,

 * and is not actually mapped anywhere at all. However, fs/buffer.c does

 * this when it notices that somebody has cleaned out all the buffers on a

 * page without actually doing it through the VM. Can you say "ext3 is

 * horribly ugly"? Thought you could.

 */

void cancel_dirty_page(struct page *page)

{

	if (TestClearPageDirty(page))

		account_page_cleaned(page, page_mapping(page));

}

EXPORT_SYMBOL(cancel_dirty_page);



/*

 * Clear a page's dirty flag, while caring for dirty memory accounting.

 * Returns true if the page was previously dirty.

mm/truncate.c

+1 −3
Original line number Diff line number Diff line
@@ -116,9 +116,7 @@ truncate_complete_page(struct address_space *mapping, struct page *page) 
	 * the VM has canceled the dirty bit (eg ext3 journaling).

	 * Hence dirty accounting check is placed after invalidation.

	 */

	if (TestClearPageDirty(page))

		account_page_cleaned(page, mapping);



	cancel_dirty_page(page);

	ClearPageMappedToDisk(page);

	delete_from_page_cache(page);

	return 0;

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