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Date: Fri, 01 Dec 2006 08:18:13 +1100 From: Nick Piggin <nickpiggin@...oo.com.au> To: Aubrey <aubreylee@...il.com> CC: Sonic Zhang <sonic.adi@...il.com>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, linux-kernel@...r.kernel.org, linux-mm@...ck.org, vapier.adi@...il.com Subject: Re: The VFS cache is not freed when there is not enough free memory to allocate Aubrey wrote: > On 11/29/06, Nick Piggin <nickpiggin@...oo.com.au> 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 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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