From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <462BFAF3.4040509@yahoo.com.au> Date: Mon, 23 Apr 2007 10:16:51 +1000 From: Nick Piggin MIME-Version: 1.0 Subject: Re: [PATCH] lazy freeing of memory through MADV_FREE References: <46247427.6000902@redhat.com> <20070420135715.f6e8e091.akpm@linux-foundation.org> <462932BE.4020005@redhat.com> <20070420150618.179d31a4.akpm@linux-foundation.org> <4629524C.5040302@redhat.com> <462ACA40.8070407@yahoo.com.au> <462B0156.9020407@redhat.com> In-Reply-To: <462B0156.9020407@redhat.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Rik van Riel Cc: Andrew Morton , linux-kernel , linux-mm , shak List-ID: Rik van Riel wrote: > Nick Piggin wrote: > >> Rik van Riel wrote: >>> Here are the transactions/seconds for each combination: >>> >>> vanilla new glibc madv_free kernel madv_free + mmap_sem >>> threads >>> >>> 1 610 609 596 545 >>> 2 1032 1136 1196 1200 >>> 4 1070 1128 2014 2024 >>> 8 1000 1088 1665 2087 >>> 16 779 1073 1310 1999 >> >> >> >> Is "new glibc" meaning MADV_DONTNEED + kernel with mmap_sem patch? > > > No, that's just the glibc change, with a vanilla kernel. OK. That would be interesting to see with the mmap_sem change, because that should increase scalability. > The third column is glibc change + mmap_sem patch. > > The fourth column has your patch in it, too. > >> The strange thing with your madv_free kernel is that it doesn't >> help single-threaded performance at all. So that work to avoid >> zeroing the new page is not a win at all there (maybe due to the >> cache effects I was worried about?). > > > Well, your patch causes the performance to drop from > 596 transactions/second to 545. Your patch is the only > difference between the third and the fourth column. Yeah. That's funny, because it means either there is some contention on the mmap_sem (or ptl) at 1 thread, or that my patch alters the uncontended performance. >> However MADV_FREE does improve scalability, which is interesting. >> The most likely reason I can see why that may be the case is that >> it avoids mmap_sem when faulting pages back in (I doubt it is due >> to avoiding the page allocator, but maybe?). >> >> So where is the down_write coming from in this workload, I wonder? >> Heap management? What syscalls? > > > I wonder if the increased parallelism simply caused > more cache line bouncing, with bounces happening in > some inner loop instead of an outer loop. > > Btw, it is quite possible that the MySQL sysbench > thing gives different results on your system. It > would be good to know what it does on a real SMP > system, vs. a single quad-core chip :) > > Other architectures would be interesting to know, > too. I don't see why parallelism should come into it at 1 thread, unless MySQL is parallelising individual transactions. Anyway, I'll try to do some more digging. -- SUSE Labs, Novell Inc. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org