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authorDaisuke Nishimura <nishimura@mxp.nes.nec.co.jp>2009-09-21 17:02:50 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2009-09-22 07:17:35 -0700
commit31a5639623a487d6db996c8138c9e53fef2e2d91 (patch)
tree4fff22b4a0333df084a6cd89e8ecbc332dbfa299 /mm/shmem.c
parent8fbb398f5c78832ee61e0d5ed0793fa8857bd853 (diff)
mm: add_to_swap_cache() must not sleep
After commit 355cfa73 ("mm: modify swap_map and add SWAP_HAS_CACHE flag"), read_swap_cache_async() will busy-wait while a entry doesn't exist in swap cache but it has SWAP_HAS_CACHE flag. Such entries can exist on add/delete path of swap cache. On add path, add_to_swap_cache() is called soon after SWAP_HAS_CACHE flag is set, and on delete path, swapcache_free() will be called (SWAP_HAS_CACHE flag is cleared) soon after __delete_from_swap_cache() is called. So, the busy-wait works well in most cases. But this mechanism can cause soft lockup if add_to_swap_cache() sleeps and read_swap_cache_async() tries to swap-in the same entry on the same cpu. This patch calls radix_tree_preload() before swapcache_prepare() and divides add_to_swap_cache() into two part: radix_tree_preload() part and radix_tree_insert() part(define it as __add_to_swap_cache()). Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Balbir Singh <balbir@linux.vnet.ibm.com> Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk> Cc: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/shmem.c')
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