On Tue, Sep 10, 2013 at 4:53 PM, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:
>
> list_lru_add() can fail if it's already on the list; leaving the counter
> alone should've been conditional on that, setting the flag - no. Said
> that, it probably should be WARN_ON(!...); this_cpu_inc(); ... |= ...;
That WARN_ON_(!..) might indeed be better (maybe just WARN_ON_ONCE())..
That DCACHE_LRU_LIST bit needs to be coherent with "the dentry->d_lru
entry is on _some_ list" (whether it's the dentry one or the shrinker
one), so if that list_lru_add() ever fails, that would be a sign of
badness.
And that whole function is very performance-critical, to the point
where we not only don't want to call down to list_lry_add(), we don't
even want to touch the d_lru list entry itself to even _look_ if it's
empty or not, because that will take a cache miss. Which was obviously
the whole reason for that DCACHE_LRU_LIST bit existing...
Linus
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