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writeback: reset wb_domain->dirty_limit[_tstmp] when memcg domain size changes

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The amount of available memory to a memcg wb_domain can change as
memcg configuration changes.  A domain's ->dirty_limit exists to
smooth out sudden drops in dirty threshold; however, when a domain's
size actually drops significantly, it hinders the dirty throttling
from adjusting to the new configuration leading to unexpected
behaviors including unnecessary OOM kills.

This patch resolves the issue by adding wb_domain_size_changed() which
resets ->dirty_limit[_tstmp] and making memcg call it on configuration
changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jan Kara <jack@suse.cz>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Greg Thelen <gthelen@google.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Tejun Heo 2015-05-22 18:23:34 -04:00 • committed by Jens Axboe
parent 841710aa6e
commit 2529bb3aad
2 changed files with 32 additions and 0 deletions
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20
include/linux/writeback.h
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@ -132,6 +132,26 @@ struct wb_domain {
unsigned long dirty_limit;
};
/**
* wb_domain_size_changed - memory available to a wb_domain has changed
* @dom: wb_domain of interest
*
* This function should be called when the amount of memory available to
* @dom has changed. It resets @dom's dirty limit parameters to prevent
* the past values which don't match the current configuration from skewing
* dirty throttling. Without this, when memory size of a wb_domain is
* greatly reduced, the dirty throttling logic may allow too many pages to
* be dirtied leading to consecutive unnecessary OOMs and may get stuck in
* that situation.
*/
static inline void wb_domain_size_changed(struct wb_domain *dom)
{
spin_lock(&dom->lock);
dom->dirty_limit_tstamp = jiffies;
dom->dirty_limit = 0;
spin_unlock(&dom->lock);
}
/*
* fs/fs-writeback.c
*/