Messages in this thread |  | | | Date | Tue, 10 Aug 2004 16:50:10 -0300 | | From | Marcelo Tosatti <> | | Subject | Re: [PATCH] reserved buffers only for PF_MEMALLOC |
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On Tue, Aug 10, 2004 at 03:42:32PM -0500, Matt Domsch wrote: > On Tue, Aug 10, 2004 at 04:04:55PM -0300, Marcelo Tosatti wrote: > > On Tue, Aug 10, 2004 at 01:20:24PM -0400, Rik van Riel wrote: > > > > > > The buffer allocation path in 2.4 has a long standing bug, > > > where non-PF_MEMALLOC tasks can dig into the reserved pool > > > in get_unused_buffer_head(). The following patch makes the > > > reserved pool only accessible to PF_MEMALLOC tasks. > > > > Out of curiosity: Do you actually seen any practical problem due to > > get_unused_buffer_head() calls eating into the reserved pool? > > > > Or have any testcase which would trigger a problem (OOM) due to it? > > My team has seen an application which mallocs as much memory as > possible, up to 95% of system RAM, using multiple processes as > necessary, and then has threads which touch all the malloc'd bytes and > threads which touch all the malloc'd pages. It keeps kswapd pretty > busy, such that you can get down to zero free and inactive clean > ZONE_NORMAL pages from which to allocate additional buffer_heads for > swapout, deadlocking the system. > > We believe that by limiting the use of the reserved buffer_head pool > to PF_MEMALLOC tasks like kswapd, kswapd can make forward progress > even in extremely low memory situations.
OK, makes sense. I assume Rik's patch fixes the deadlock you are seeing?
Have you tested it?
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