On Sun, 2006-12-17 at 15:40 -0800, Andrew Morton wrote:
> On Sun, 17 Dec 2006 15:39:32 +0200
> Andrei Popa <[email protected]> wrote:
>
> > I was mistaken, I'm still having file corruption with rtorrent.
> >
>
> Well I'm not very optimistic, but if people could try this, please...
>
>
>
> From: Andrew Morton <[email protected]>
>
> try_to_free_buffers() clears the page's dirty state if it successfully removed
> the page's buffers.
>
> Background for this:
>
> - a process does a one-byte-write to a file on a 64k pagesize, 4k
> blocksize ext3 filesystem. The page is now PageDirty, !PgeUptodate and
> has one dirty buffer and 15 not uptodate buffers.
>
> - kjournald writes the dirty buffer. The page is now PageDirty,
> !PageUptodate and has a mix of clean and not uptodate buffers.
>
> - try_to_free_buffers() removes the page's buffers. It MUST now clear
> PageDirty. If we were to leave the page dirty then we'd have a dirty, not
> uptodate page with no buffer_heads.
>
> We're screwed: we cannot write the page because we don't know which
> sections of it contain garbage. We cannot read the page because we don't
> know which sections of it contain modified data. We cannot free the page
> because it is dirty.
>
How about we stick something like this on top of that patch. It should
preserve the dirty state as required.
I tried to tinker with avoiding the clear/set thing but could not
convince myself it was close to safe.
This should be safe; page_mkclean walks the rmap and flips the pte's
under the pte lock and records the dirty state while iterating.
Concurrent faults will either do set_page_dirty() before we get around
to doing it or vice versa, but dirty state is not lost.
---
mm/page-writeback.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
Index: linux-2.6-git/mm/page-writeback.c
===================================================================
--- linux-2.6-git.orig/mm/page-writeback.c 2006-12-18 17:24:41.000000000 +0100
+++ linux-2.6-git/mm/page-writeback.c 2006-12-18 17:26:56.000000000 +0100
@@ -872,8 +872,9 @@ int test_clear_page_dirty(struct page *p
* page is locked, which pins the address_space
*/
if (mapping_cap_account_dirty(mapping)) {
- if (must_clean_ptes)
- page_mkclean(page);
+ int cleaned = page_mkclean(page);
+ if (!must_clean_ptes && cleaned)
+ set_page_dirty(page);
dec_zone_page_state(page, NR_FILE_DIRTY);
}
return 1;
-
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