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13 June 2022, 11:31:42 UTC
Revision 32c5fc10e79a7053ac5728b01a0bff55cbcb9d49 authored by Bo Liu on 02 November 2009, 16:50:33 UTC, committed by Linus Torvalds on 02 November 2009, 17:44:41 UTC 
mm: remove incorrect swap_count() from try_to_unuse()
 
In try_to_unuse(), swcount is a local copy of *swap_map, including the
SWAP_HAS_CACHE bit; but a wrong comparison against swap_count(*swap_map),
which masks off the SWAP_HAS_CACHE bit, succeeded where it should fail.

That had the effect of resetting the mm from which to start searching
for the next swap page, to an irrelevant mm instead of to an mm in which
this swap page had been found: which may increase search time by ~20%.
But we're used to swapoff being slow, so never noticed the slowdown.

Remove that one spurious use of swap_count(): Bo Liu thought it merely
redundant, Hugh rewrote the description since it was measurably wrong.

Signed-off-by: Bo Liu <bo-liu@hotmail.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 parent c9354c8
History
Tip revision: 32c5fc10e79a7053ac5728b01a0bff55cbcb9d49 authored by Bo Liu on 02 November 2009, 16:50:33 UTC
mm: remove incorrect swap_count() from try_to_unuse()
Tip revision: 32c5fc1
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