[lkml]   [2006]   [Dec]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [patch 03/13] io-accounting: write accounting
On Wed, 13 Dec 2006 00:45:50 -0800
Suleiman Souhlal <> wrote:

> wrote:
> > From: Andrew Morton <>
> >
> > Accounting writes is fairly simple: whenever a process flips a page from clean
> > to dirty, we accuse it of having caused a write to underlying storage of
> > PAGE_CACHE_SIZE bytes.
> On architectures where dirtying a page doesn't cause a page fault (like i386), couldn't you end up billing the wrong process (in fact, I think that even on other archituctures set_page_dirty() doesn't get called immediately in the page fault handler)?

Yes, that would be a problem in 2.6.18 and earlier.

In 2.6.19 and later, we do take a fault when transitioning a page from
pte-clean to pte-dirty. That was done to get the dirty-page accounting
right - to avoid the all-of-memory-is-dirty-but-the-kernel-doesn't-know-it

> AFAICS, set_page_dirty() is mostly called when trying to unmap a page when trying to shrink LRU lists, and there is no guarantee that this happens under the process that dirtied it (in fact, the set_page_dirty() is often done by kswapd).

hm, that code is still there in zap_pte_range(). If all is well, that
set_page_dirty() call should never return true. Peter did, you ever test
for that?

(Well, it might return true in rare races, because zap_pte_range() doesn't
lock the pages)
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

 \ /
  Last update: 2006-12-13 10:03    [W:0.039 / U:21.108 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site