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authorAndrea Arcangeli <aarcange@redhat.com>2017-07-06 15:37:08 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2017-07-06 16:24:31 -0700
commit80b18dfa53bbb03085eba6401f5d29dad49205b7 (patch)
tree756c3a06ab0aa20523ef525ba65c40d58c4478f4 /drivers
parent8dc5ffcd5a74da39ed2c533d786a3f78671a38b8 (diff)
ksm: optimize refile of stable_node_dup at the head of the chain
If a candidate stable_node_dup has been found and it can accept further merges it can be refiled to the head of the list to speedup next searches without altering which dup is found and how the dups accumulate in the chain. We already refiled it back to the head in the prune_stale_stable_nodes case, but we didn't refile it if not pruning (which is more common). And we also refiled it when it was already at the head which is unnecessary (in the prune_stale_stable_nodes case, nr > 1 means there's more than one dup in the chain, it doesn't mean it's not already at the head of the chain). The stable_node_chain list is single threaded and there's no SMP locking contention so it should be faster to refile it to the head of the list also if prune_stale_stable_nodes is false. Profiling shows the refile happens 1.9% of the time when a dup is found with a max_page_sharing limit setting of 3 (with max_page_sharing of 2 the refile never happens of course as there's never space for one more merge) which is reasonably low. At higher max_page_sharing values it should be much less frequent. This is just an optimization. Link: http://lkml.kernel.org/r/20170518173721.22316-4-aarcange@redhat.com Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Cc: Evgheni Dereveanchin <ederevea@redhat.com> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: Petr Holasek <pholasek@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Arjan van de Ven <arjan@linux.intel.com> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Gavin Guo <gavin.guo@canonical.com> Cc: Jay Vosburgh <jay.vosburgh@canonical.com> Cc: Mel Gorman <mgorman@techsingularity.net> Cc: Dan Carpenter <dan.carpenter@oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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