Messages in this thread | | | Date | Mon, 17 Oct 2011 13:14:23 -0700 (PDT) | From | Dan Magenheimer <> | Subject | RE: [PATCH] staging: zcache: remove zcache_direct_reclaim_lock |
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> From: Dan Magenheimer > Sent: Wednesday, October 12, 2011 2:39 PM > To: Seth Jennings; gregkh@suse.de > Cc: cascardo@holoscopio.com; rdunlap@xenotime.net; devel@driverdev.osuosl.org; linux- > kernel@vger.kernel.org; linux-mm@kvack.org; rcj@linux.vnet.ibm.com; brking@linux.vnet.ibm.com > Subject: RE: [PATCH] staging: zcache: remove zcache_direct_reclaim_lock > > > From: Seth Jennings [mailto:sjenning@linux.vnet.ibm.com] > > Subject: [PATCH] staging: zcache: remove zcache_direct_reclaim_lock > > > > zcache_do_preload() currently does a spin_trylock() on the > > zcache_direct_reclaim_lock. Holding this lock intends to prevent > > shrink_zcache_memory() from evicting zbud pages as a result > > of a preload. > > > > However, it also prevents two threads from > > executing zcache_do_preload() at the same time. The first > > thread will obtain the lock and the second thread's spin_trylock() > > will fail (an aborted preload) causing the page to be either lost > > (cleancache) or pushed out to the swap device (frontswap). It > > also doesn't ensure that the call to shrink_zcache_memory() is > > on the same thread as the call to zcache_do_preload(). > > Yes, this looks to be leftover code from early in kztmem/zcache > development. Good analysis. > > > Additional, there is no need for this mechanism because all > > zcache_do_preload() calls that come down from cleancache already > > have PF_MEMALLOC set in the process flags which prevents > > direct reclaim in the memory manager. If the zcache_do_preload() > > Might it be worthwhile to add a BUG/ASSERT for the presence > of PF_MEMALLOC, or at least a comment in the code? > > > call is done from the frontswap path, we _want_ reclaim to be > > done (which it isn't right now). > > > > This patch removes the zcache_direct_reclaim_lock and related > > statistics in zcache. > > > > Based on v3.1-rc8 > > > > Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com> > > Reviewed-by: Dave Hansen <dave@linux.vnet.ibm.com> > > With added code/comment per above... > Acked-by: Dan Magenheimer <dan.magenheimer@oracle.com>
After Seth's further analysis, ignore my conditional and consider v1 of this patch:
Acked-by: Dan Magenheimer <dan.magenheimer@oracle.com>
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