Messages in this thread | | | Date | Mon, 22 Feb 2010 15:34:21 -0500 | From | Rik van Riel <> | Subject | Re: [patch 3/3] vmscan: detect mapped file pages used only once |
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On 02/22/2010 02:49 PM, Johannes Weiner wrote: > The VM currently assumes that an inactive, mapped and referenced file > page is in use and promotes it to the active list. > > However, every mapped file page starts out like this and thus a problem > arises when workloads create a stream of such pages that are used only > for a short time. By flooding the active list with those pages, the VM > quickly gets into trouble finding eligible reclaim canditates. The > result is long allocation latencies and eviction of the wrong pages. > > This patch reuses the PG_referenced page flag (used for unmapped file > pages) to implement a usage detection that scales with the speed of > LRU list cycling (i.e. memory pressure). > > If the scanner encounters those pages, the flag is set and the page > cycled again on the inactive list. Only if it returns with another > page table reference it is activated. Otherwise it is reclaimed as > 'not recently used cache'. > > This effectively changes the minimum lifetime of a used-once mapped > file page from a full memory cycle to an inactive list cycle, which > allows it to occur in linear streams without affecting the stable > working set of the system. > > Signed-off-by: Johannes Weiner<hannes@cmpxchg.org>
Reviewed-by: Rik van Riel <riel@redhat.com>
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