From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Wed, 28 May 2008 01:40:17 -0700 From: Andrew Morton Subject: Re: [PATCH] 2.6.26-rc: x86: pci-dma.c: use __GFP_NO_OOM instead of __GFP_NORETRY Message-Id: <20080528014017.9b3d116f.akpm@linux-foundation.org> In-Reply-To: <1211963485.28138.14.camel@localhost.localdomain> References: <20080526234940.GA1376@xs4all.net> <20080527014720.6db68517.akpm@linux-foundation.org> <20080528024727.GB20824@one.firstfloor.org> <1211963485.28138.14.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Miquel van Smoorenburg Cc: Andi Kleen , Glauber Costa , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Ingo Molnar List-ID: On Wed, 28 May 2008 10:31:25 +0200 Miquel van Smoorenburg wrote: > > When the 16MB zone overflows (which can be common in some workloads) > > calling the OOM killer is pretty useless because it has barely any > > real user data [only exception would be the "only 16MB" case Alan > > mentioned]. Killing random processes in this case is bad. > > > > I think for 16MB __GFP_NORETRY is ok because there should be > > nothing freeable in there so looping is useless. Only exception would be the > > "only 16MB total" case again but I'm not sure 2.6 supports that at all > > on x86. > > > > On the other hand d_a_c() does more allocations than just 16MB, especially > > on 64bit and the other zones need different strategies. > > Okay, so how about this then ? > > --- linux-2.6.26-rc4.orig/arch/x86/kernel/pci-dma.c 2008-05-26 20:08:11.000000000 +0200 > +++ linux-2.6.26-rc4/arch/x86/kernel/pci-dma.c 2008-05-28 10:27:41.000000000 +0200 > @@ -397,9 +397,6 @@ > if (dev->dma_mask == NULL) > return NULL; > > - /* Don't invoke OOM killer */ > - gfp |= __GFP_NORETRY; > - > #ifdef CONFIG_X86_64 > /* Why <=? Even when the mask is smaller than 4GB it is often > larger than 16MB and in this case we have a chance of > @@ -410,7 +407,9 @@ > #endif > > again: > - page = dma_alloc_pages(dev, gfp, get_order(size)); > + /* Don't invoke OOM killer or retry in lower 16MB DMA zone */ > + page = dma_alloc_pages(dev, > + (gfp & GFP_DMA) ? gfp | __GFP_NORETRY : gfp, get_order(size)); > if (page == NULL) > return NULL; I guess that's more specifally solving that-which-we-wish-to-solve. Formally we should be testing __GFP_DMA here, not GFP_DMA - just the zone selector field. They're presently equal, but someone could legitimately come along and do #define GFP_DMA (__GFP_DMA|__GFP_HIGH) or similar. -- 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