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Date: Wed, 21 May 2014 23:33:54 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Andrew Morton <akpm@...ux-foundation.org> Cc: Mel Gorman <mgorman@...e.de>, Oleg Nesterov <oleg@...hat.com>, Johannes Weiner <hannes@...xchg.org>, Vlastimil Babka <vbabka@...e.cz>, Jan Kara <jack@...e.cz>, Michal Hocko <mhocko@...e.cz>, Hugh Dickins <hughd@...gle.com>, Dave Hansen <dave.hansen@...el.com>, Linux Kernel <linux-kernel@...r.kernel.org>, Linux-MM <linux-mm@...ck.org>, Linux-FSDevel <linux-fsdevel@...r.kernel.org>, Paul McKenney <paulmck@...ux.vnet.ibm.com>, Linus Torvalds <torvalds@...ux-foundation.org>, David Howells <dhowells@...hat.com> Subject: Re: [PATCH] mm: filemap: Avoid unnecessary barries and waitqueue lookups in unlock_page fastpath v5 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.. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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