On Fri, Jun 14, 2013 at 12:16:47PM -0400, Rik van Riel wrote: > On 06/06/2013 01:37 PM, Rik van Riel wrote: > >On 06/06/2013 05:04 AM, Mel Gorman wrote: > >>On Wed, Jun 05, 2013 at 05:10:31PM +0200, Andrea Arcangeli wrote: > >>>Zone reclaim locked breaks zone_reclaim_mode=1. If more than one > >>>thread allocates memory at the same time, it forces a premature > >>>allocation into remote NUMA nodes even when there's plenty of clean > >>>cache to reclaim in the local nodes. > >>> > >>>Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx> > >> > >>Be aware that after this patch is applied that it is possible to have a > >>situation like this > >> > >>1. 4 processes running on node 1 > >>2. Each process tries to allocate 30% of memory > >>3. Each process reads the full buffer in a loop (stupid, just an example) > >> > >>In this situation the processes will continually interfere with each > >>other until one of them gets migrated to another zone by the scheduler. > > > >This is a very good point. > > > >Andrea, I suspect we will need some kind of safeguard against > >this problem. > > Never mind me. > > In __zone_reclaim we set the flags in swap_control so > we never unmap pages or swap pages out at all by > default, so this should not be an issue at all. > > In order to get the problem illustrated above, the > user will have to enable RECLAIM_SWAP through sysfs > manually. > For the mapped case and the default tuning for zone_reclaim_mode then yes. If instead of allocating 30% of memory the processes are using using buffered reads/writes then they'll reach each others page cache pages and it's a very similar problem. -- Mel Gorman SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>