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bcache: Document shrinker reserve better

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Signed-off-by: Kent Overstreet <kmo@daterainc.com>
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Kent Overstreet 2013-06-03 13:04:56 -07:00 committed by Kent Overstreet
parent e49c7c374e
commit 36c9ea9837
1 changed files with 7 additions and 0 deletions
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7
drivers/md/bcache/btree.c
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@ -622,6 +622,13 @@ static int bch_mca_shrink(struct shrinker *shrink, struct shrink_control *sc)
else if (!mutex_trylock(&c->bucket_lock))
return -1;
/*
* It's _really_ critical that we don't free too many btree nodes - we
* have to always leave ourselves a reserve. The reserve is how we
* guarantee that allocating memory for a new btree node can always
* succeed, so that inserting keys into the btree can always succeed and
* IO can always make forward progress:
*/
nr /= c->btree_pages;
nr = min_t(unsigned long, nr, mca_can_free(c));