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H A D | truncate.c | diff a2b345642f530054a92b8d2b5108436225a8093e Tue Feb 05 07:29:28 CET 2008 Bjorn Steinbrink <B.Steinbrink@gmx.de> Fix dirty page accounting leak with ext3 data=journal
In 46d2277c796f9f4937bfa668c40b2e3f43e93dd0 ("Clean up and make try_to_free_buffers() not race with dirty pages"), try_to_free_buffers was changed to bail out if the page was dirty.
That in turn caused truncate_complete_page to leak massive amounts of memory, because the dirty bit was only cleared after the call to try_to_free_buffers.
So the call to cancel_dirty_page was moved up to have the dirty bit cleared early in 3e67c0987d7567ad666641164a153dca9a43b11d ("truncate: clear page dirtiness before running try_to_free_buffers()").
The problem with that fix is, that the page can be redirtied after cancel_dirty_page was called, eg. like this:
truncate_complete_page() cancel_dirty_page() // PG_dirty cleared, decr. dirty pages do_invalidatepage() ext3_invalidatepage() journal_invalidatepage() journal_unmap_buffer() __dispose_buffer() __journal_unfile_buffer() __journal_temp_unlink_buffer() mark_buffer_dirty(); // PG_dirty set, incr. dirty pages
And then we end up with dirty pages being wrongly accounted.
As a result, in ecdfc9787fe527491baefc22dce8b2dbd5b2908d ("Resurrect 'try_to_free_buffers()' VM hackery") the changes to try_to_free_buffers were reverted, so the original reason for the massive memory leak is gone, and we can also revert the move of the call to cancel_dirty_page from truncate_complete_page and get the accounting right again.
I'm not sure if it matters, but opposed to the final check in __remove_from_page_cache, this one also cares about the task io accounting, so maybe we want to use this instead, although it's not quite the clean fix either.
Signed-off-by: Björn Steinbrink <B.Steinbrink@gmx.de> Tested-by: Krzysztof Piotr Oledzki <ole@ans.pl> Cc: Jan Kara <jack@ucw.cz> Cc: Nick Piggin <nickpiggin@yahoo.com.au> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Thomas Osterried <osterried@jesse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> diff 3e67c0987d7567ad666641164a153dca9a43b11d Thu Dec 21 20:00:33 CET 2006 Andrew Morton <akpm@osdl.org> [PATCH] truncate: clear page dirtiness before running try_to_free_buffers()
truncate presently invalidates the dirty page's buffer_heads then shoots down the page. But try_to_free_buffers() will now bale out because the page is dirty.
Net effect: the LRU gets filled with dirty pages which have invalidated buffer_heads attached. They have no ->mapping and hence cannot be cleaned. The machine leaks memory at an enormous rate.
Fix this by cleaning the page before running try_to_free_buffers(), so try_to_free_buffers() can do its work.
Also, remember to do dirty-page-acoounting in cancel_dirty_page() so the machine won't wedge up trying to write non-existent dirty pages.
Probably still wrong, but now less so.
Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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