From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <456F4A95.2090503@yahoo.com.au> Date: Fri, 01 Dec 2006 08:18:13 +1100 From: Nick Piggin MIME-Version: 1.0 Subject: Re: The VFS cache is not freed when there is not enough free memory to allocate References: <6d6a94c50611212351if1701ecx7b89b3fe79371554@mail.gmail.com> <1164185036.5968.179.camel@twins> <6d6a94c50611220202t1d076b4cye70dcdcc19f56e55@mail.gmail.com> <456A964D.2050004@yahoo.com.au> <4e5ebad50611282317r55c22228qa5333306ccfff28e@mail.gmail.com> <6d6a94c50611290127u2b26976en1100217a69d651c0@mail.gmail.com> <456D5347.3000208@yahoo.com.au> <6d6a94c50611300454g22196d2frec54e701abaebf17@mail.gmail.com> In-Reply-To: <6d6a94c50611300454g22196d2frec54e701abaebf17@mail.gmail.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Aubrey Cc: Sonic Zhang , Peter Zijlstra , linux-kernel@vger.kernel.org, linux-mm@kvack.org, vapier.adi@gmail.com List-ID: Aubrey wrote: > On 11/29/06, Nick Piggin wrote: > >> That was the order-9 allocation failure. Which is not going to be >> solved properly by just dropping caches. >> >> But Sonic apparently saw failures with 4K allocations, where the >> caches weren't getting shrunk properly. This would be more interesting >> because it would indicate a real problem with the kernel. >> > I have done several test cases. when cat /proc/meminfo show MemFree < > 8192KB, > > 1) malloc(1024 * 4), 256 times = 8MB, allocation successful. > 2) malloc(1024 * 16), 64 times = 8MB, allocation successful. > 3) malloc(1024 * 64), 16 times = 8MB, allocation successful. > 4) malloc(1024 * 128), 8 times = 8MB, allocation failed. > 5) malloc(1024 * 256), 4 times = 8MB, allocation failed. > >> From those results, we know, when allocation <=64K, cache can be > > shrunk properly. > That means the malloc size of an application on nommu should be > <=64KB. That's exactly our problem. Some video programmes need a big > block which has contiguous physical address. But yes, as you said, we > must keep malloc not to alloc a big block to make the current kernel > working robust on nommu. > > So, my question is, Can we improve this issue? why malloc(64K) is ok > but malloc(128K) not? Is there any existing parameters about this > issue? why not kernel attempt to shrunk cache no matter how big memory > allocation is requested? > > Any thoughts? The pattern you are seeing here is probably due to the page allocator always retrying process context allocations which are <= order 3 (64K with 4K pages). You might be able to increase this limit a bit for your system, but it could easily cause problems. Especially fragmentation on nommu systems where the anonymous memory cannot be paged out. -- SUSE Labs, Novell Inc. Send instant messages to your online friends http://au.messenger.yahoo.com -- 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