Messages in this thread | | | Date | Wed, 13 Dec 2006 02:35:35 -0800 | From | Suleiman Souhlal <> | Subject | Re: [patch 03/13] io-accounting: write accounting |
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Andrew Morton wrote: > On Wed, 13 Dec 2006 00:45:50 -0800 > Suleiman Souhlal <ssouhlal@FreeBSD.org> wrote: > > >>akpm@osdl.org wrote: >> >>>From: Andrew Morton <akpm@osdl.org> >>> >>>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 > problem.
Ah yes indeed. I'm unable to keep up with all the new developments. :-(
However, if my understanding of this code is correct, it seems that the page fault is only done for shared writable VMAs, so you still can't rely on set_page_dirty() always being called by the process that dirtied the page in the first place.
Am I wrong?
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