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    SubjectRe: [BUG] infinite loop in find_get_pages()
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    On Wed, 2011-09-14 at 16:43 +0800, Eric Dumazet wrote:
    > Le mercredi 14 septembre 2011 à 16:20 +0800, Shaohua Li a écrit :
    > > 2011/9/14 Shaohua Li <shli@kernel.org>:
    > > > it appears we didn't account skipped swap entry in find_get_pages().
    > > > does the attached patch help?
    > > I can easily reproduce the issue. Just cp files in tmpfs, trigger swap and
    > > drop caches. The debug patch fixes it at my side.
    > > Eric, please try it.
    > >
    >
    > Hello Shaohua
    >
    > I tried it with added traces :
    >
    >
    > [ 277.077855] mv used greatest stack depth: 3336 bytes left
    > [ 310.558012] nr_found=2 nr_skip=2
    > [ 310.558139] nr_found=14 nr_skip=14
    > [ 332.195162] nr_found=2 nr_skip=2
    > [ 332.195274] nr_found=14 nr_skip=14
    > [ 352.315273] nr_found=14 nr_skip=14
    > [ 372.673575] nr_found=14 nr_skip=14
    > [ 397.115463] nr_found=14 nr_skip=14
    > [ 403.391694] cc1 used greatest stack depth: 3184 bytes left
    > [ 404.761194] cc1 used greatest stack depth: 2640 bytes left
    > [ 417.306510] nr_found=14 nr_skip=14
    > [ 440.198051] nr_found=14 nr_skip=14
    >
    > I also used :
    >
    > - if (unlikely(!ret && nr_found))
    > + if (unlikely(!ret && nr_found > nr_skip))
    > goto restart;
    nr_found > nr_skip is better

    > It seems to fix the bug. I suspect it also aborts
    > invalidate_mapping_pages() if we skip 14 pages, but existing comment
    > states its OK :
    >
    > /*
    > * Note: this function may get called on a shmem/tmpfs mapping:
    > * pagevec_lookup() might then return 0 prematurely (because it
    > * got a gangful of swap entries); but it's hardly worth worrying
    > * about - it can rarely have anything to free from such a mapping
    > * (most pages are dirty), and already skips over any difficulties.
    > */
    that might be a problem, let Hugh answer if it is.

    Thanks,
    Shaohua

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