[lkml]   [2009]   [Nov]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH 2/7] mmc: Don't use PF_MEMALLOC
> On Tue, 17 Nov 2009 16:17:50 +0900 (JST)
> KOSAKI Motohiro <> 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.

 \ /
  Last update: 2009-11-17 13:01    [W:0.066 / U:8.368 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site