Messages in this thread | | | Date | Wed, 21 May 2014 23:33:54 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] mm: filemap: Avoid unnecessary barries and waitqueue lookups in unlock_page fastpath v5 |
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On Wed, May 21, 2014 at 02:26:22PM -0700, Andrew Morton wrote: > > +static inline void > > +__prepare_to_wait(wait_queue_head_t *q, wait_queue_t *wait, > > + struct page *page, int state, bool exclusive) > > Putting MM stuff into core waitqueue code is rather bad. I really > don't know how I'm going to explain this to my family.
Right, so we could avoid all that and make the functions in mm/filemap.c rather large and opencode a bunch of wait.c stuff.
Which is pretty much what I initially pseudo proposed.
> > + __ClearPageWaiters(page); > > We're freeing the page - if someone is still waiting on it then we have > a huge bug? It's the mysterious collision thing again I hope?
Yeah, so we only clear that bit when at 'unlock' we find there are no more pending waiters, so if the last unlock still had a waiter, we'll leave the bit set. So its entirely reasonable to still have it set when we free a page etc..
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