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authorJens Axboe <axboe@kernel.dk>2017-09-28 11:31:55 -0600
committerJens Axboe <axboe@kernel.dk>2017-10-03 08:38:17 -0600
commitaac8d41cd438f25bf3110fc6b98f1d16d7dbc169 (patch)
tree0c507b3a603955686e9b2cd13c5fcbbcc638ed6d /include
parente8e8a0c6c9bfc0b320671166dd795f413f636773 (diff)
writeback: only allow one inflight and pending full flush
When someone calls wakeup_flusher_threads() or wakeup_flusher_threads_bdi(), they schedule writeback of all dirty pages in the system (or on that bdi). If we are tight on memory, we can get tons of these queued from kswapd/vmscan. This causes (at least) two problems: 1) We consume a ton of memory just allocating writeback work items. We've seen as much as 600 million of these writeback work items pending. That's a lot of memory to pointlessly hold hostage, while the box is under memory pressure. 2) We spend so much time processing these work items, that we introduce a softlockup in writeback processing. This is because each of the writeback work items don't end up doing any work (it's hard when you have millions of identical ones coming in to the flush machinery), so we just sit in a tight loop pulling work items and deleting/freeing them. Fix this by adding a 'start_all' bit to the writeback structure, and set that when someone attempts to flush all dirty pages. The bit is cleared when we start writeback on that work item. If the bit is already set when we attempt to queue !nr_pages writeback, then we simply ignore it. This provides us one full flush in flight, with one pending as well, and makes for more efficient handling of this type of writeback. Acked-by: Johannes Weiner <hannes@cmpxchg.org> Tested-by: Chris Mason <clm@fb.com> Reviewed-by: Jan Kara <jack@suse.cz> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'include')
-rw-r--r--include/linux/backing-dev-defs.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h
index 866c433e7d32..420de5c7c7f9 100644
--- a/include/linux/backing-dev-defs.h
+++ b/include/linux/backing-dev-defs.h
@@ -24,6 +24,7 @@ enum wb_state {
WB_shutting_down, /* wb_shutdown() in progress */
WB_writeback_running, /* Writeback is in progress */
WB_has_dirty_io, /* Dirty inodes on ->b_{dirty|io|more_io} */
+ WB_start_all, /* nr_pages == 0 (all) work pending */
};
enum wb_congested_state {