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    SubjectRe: [PATCH 12/12] vmscan: Do not writeback pages in direct reclaim
    On 06/15/2010 07:45 AM, Mel Gorman wrote:
    > On Mon, Jun 14, 2010 at 05:55:51PM -0400, Rik van Riel wrote:
    >> On 06/14/2010 07:17 AM, Mel Gorman wrote:
    >>
    >>> diff --git a/mm/vmscan.c b/mm/vmscan.c
    >>> index 4856a2a..574e816 100644
    >>> --- a/mm/vmscan.c
    >>> +++ b/mm/vmscan.c
    >>> @@ -372,6 +372,12 @@ int write_reclaim_page(struct page *page, struct address_space *mapping,
    >>> return PAGE_SUCCESS;
    >>> }
    >>>
    >>> +/* kswapd and memcg can writeback as they are unlikely to overflow stack */
    >>> +static inline bool reclaim_can_writeback(struct scan_control *sc)
    >>> +{
    >>> + return current_is_kswapd() || sc->mem_cgroup != NULL;
    >>> +}
    >>> +
    >>
    >> I'm not entirely convinced on this bit, but am willing to
    >> be convinced by the data.
    >>
    >
    > Which bit?
    >
    > You're not convinced that kswapd should be allowed to write back?
    > You're not convinced that memcg should be allowed to write back?
    > You're not convinced that direct reclaim writing back pages can overflow
    > the stack?

    If direct reclaim can overflow the stack, so can direct
    memcg reclaim. That means this patch does not solve the
    stack overflow, while admitting that we do need the
    ability to get specific pages flushed to disk from the
    pageout code.

    --
    All rights reversed


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