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    SubjectRe: [PATCH 2/7] mmc: Don't use PF_MEMALLOC
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    > On Tue, 17 Nov 2009 16:17:50 +0900 (JST)
    > KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote:
    >
    > > Non MM subsystem must not use PF_MEMALLOC. Memory reclaim need few
    > > memory, anyone must not prevent it. Otherwise the system cause
    > > mysterious hang-up and/or OOM Killer invokation.
    >
    > So now what happens if we are paging and all our memory is tied up for
    > writeback to a device or CIFS etc which can no longer allocate the memory
    > to complete the write out so the MM can reclaim ?

    Probably my answer is not so simple. sorry.

    reason1: MM reclaim does both dropping clean memory and writing out dirty pages.
    reason2: if all memory is exhausted, maybe we can't recover it. it is
    fundamental limitation of Virtual Memory subsystem. and, min-watermark is
    decided by number of system physcal memory, but # of I/O issue (i.e. # of
    pages of used by writeback thread) is mainly decided # of devices.
    then, we can't gurantee min-watermark is sufficient on any systems.
    Only reasonable solution is mempool like reservation, I think.
    IOW, any reservation memory shouldn't share unrelated subsystem. otherwise
    we lost any gurantee.

    So, I think we need to hear why many developer don't use mempool,
    instead use PF_MEMALLOC.

    > Am I missing something or is this patch set not addressing the case where
    > the writeback thread needs to inherit PF_MEMALLOC somehow (at least for
    > the I/O in question and those blocking it)

    Yes, probably my patchset isn't perfect. honestly I haven't understand
    why so many developer prefer to use PF_MEMALLOC.





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