From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: [PATCH 3/6] compcache: TLSF Allocator interface From: Peter Zijlstra In-Reply-To: <4cefeab80803241034m6f62c01fq669129db9959f47f@mail.gmail.com> References: <200803242034.24264.nitingupta910@gmail.com> <1206377777.6437.123.camel@lappy> <4cefeab80803241034m6f62c01fq669129db9959f47f@mail.gmail.com> Content-Type: text/plain Date: Mon, 24 Mar 2008 19:56:53 +0100 Message-Id: <1206385013.6437.140.camel@lappy> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Nitin Gupta Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: On Mon, 2008-03-24 at 23:04 +0530, Nitin Gupta wrote: > On Mon, Mar 24, 2008 at 10:26 PM, Peter Zijlstra wrote: > > On Mon, 2008-03-24 at 20:34 +0530, Nitin Gupta wrote: > > > Two Level Segregate Fit (TLSF) Allocator is used to allocate memory for > > > variable size compressed pages. Its fast and gives low fragmentation. > > > Following links give details on this allocator: > > > - http://rtportal.upv.es/rtmalloc/files/tlsf_paper_spe_2007.pdf > > > - http://code.google.com/p/compcache/wiki/TLSFAllocator > > > > > > This kernel port of TLSF (v2.3.2) introduces several changes but underlying > > > algorithm remains the same. > > > > > > Changelog TLSF v2.3.2 vs this kernel port > > > - Pool now dynamically expands/shrinks. > > > It is collection of contiguous memory regions. > > > - Changes to pool create interface as a result of above change. > > > - Collect and export stats (/proc/tlsfinfo) > > > - Cleanups: kernel coding style, added comments, macros -> static inline, etc. > > > > Can you explain why you need this allocator, why don't the current > > kernel allocators work for you? > > > > > > kmalloc() allocates one of pre-defined sizes (as defined in > kmalloc_sizes.h). This will surely cause severe fragmentation with > these variable sized compressed pages. > > Whereas, TLSF maintains very fine grained size lists. In all the > workloads I tested, it showed <5% fragmentation. Also, its very simple > as just ~700 LOC. Yeah, it also suffers from a horrible coding style, can use excessive amounts of vmalloc space, isn't hooked into the reclaim process as an allocator should be and has a severe lack of per-cpu data making it a pretty big bottleneck on anything with more than a few cores. Now, it might be needed, might work better, and the scalability issue might not be a problem when used for swap, but still, you don't treat any of these points in your changelog. FWIW, please split up the patches in a sane way. This series looks like it wants to be 2 or 3 patches. The first introducing all of TLSF (this split per file is horrible). The second doing all of the block device, and a possible last doing documentation and such. Also, how bad was kmalloc() compared to this TLSF, we need numbers :-) -- 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