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Date: Thu, 13 May 2010 18:05:25 +0900 (JST) From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> To: Jiri Slaby <jslaby@...e.cz> Cc: kosaki.motohiro@...fujitsu.com, Changli Gao <xiaosuo@...il.com>, akpm@...ux-foundation.org, Eric Dumazet <eric.dumazet@...il.com>, Alexander Viro <viro@...iv.linux.org.uk>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, Alexey Dobriyan <adobriyan@...il.com>, Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>, linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, Avi Kivity <avi@...hat.com>, Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp> Subject: Re: [RFC] mm: generic adaptive large memory allocation APIs Hi > > Hi > > > >> void *kvmalloc(size_t size) > >> { > >> void *ptr; > >> > >> if (size < PAGE_SIZE) > >> return kmalloc(PAGE_SIZE, GFP_KERNEL); > >> ptr = alloc_pages_exact(size, GFP_KERNEL | __GFP_NOWARN); > > > > low order GFP_KERNEL allocation never fail. then, this doesn't works > > as you expected. > > Hi, I suppose you mean the kmalloc allocation -- so kmalloc should fail > iff alloc_pages_exact (unless somebody frees a heap of memory indeed)? I mean, if size of alloc_pages_exact() argument is less than 8 pages, alloc_pages_exact() never fail. see __alloc_pages_slowpath(). > > >> if (ptr != NULL) > >> return ptr; > >> > >> return vmalloc(size); > > > > On x86, vmalloc area is only 128MB address space. it is very rare > > resource than physical ram. vmalloc fallback is not good idea. > > These functions are a replacement for explicit > if (!(x = kmalloc())) > x = vmalloc(); > ... > if (is_vmalloc(x)) > vfree(x); > else > kfree(x); > in the code (like fdtable does this). > > The 128M limit on x86_32 for vmalloc is configurable so if drivers in > sum need more on some specific hardware, it can be increased on the > command line (I had to do this on one machine in the past). Right, but 99% end user don't do this. I don't think this is effective advise. > Anyway as this is a replacement for explicit tests, it shouldn't change > the behaviour in any way. Obviously when a user doesn't need virtually > contiguous space, he shouldn't use this interface at all. Why can't we make fdtable virtually contiguous free? Anyway, alloc_fdmem() also don't works as author expected. -- 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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