From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Tue, 27 May 2008 01:47:20 -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: <20080527014720.6db68517.akpm@linux-foundation.org> In-Reply-To: <20080526234940.GA1376@xs4all.net> References: <20080526234940.GA1376@xs4all.net> 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 Tue, 27 May 2008 01:49:47 +0200 Miquel van Smoorenburg wrote: > Please consider the below patch for 2.6.26 (can somebody from the > x86 team pick this up please? Thank you) > > > > [PATCH] 2.6.26-rc: x86: pci-dma.c: use __GFP_NO_OOM instead of __GFP_NORETRY > > arch/x86/kernel/pci-dma.c::dma_alloc_coherent() adds __GFP_NORETRY to > the gfp flags before calling alloc_pages() to prevent the oom killer > from running. Now, why does dma_alloc_coherent() do that? If __GFP_FS is cleared (most cases) then we won't be calling out_of_memory() anyway. If __GFP_FS _is_ set then setting __GFP_NORETRY will do much more than avoiding oom-killings. It will prevent the page allocator from retrying and will cause the problems which one assumes (without evidence :() you have observed. So... why not just remove the setting of __GFP_NORETRY? Why is it wrong to oom-kill things in this case? > This has the expected side effect that that alloc_pages() doesn't > retry anymore. Not really a problem for dma_alloc_coherent(.. GFP_ATOMIC) > which is the way most drivers use it (through pci_alloc_consistent()) > but drivers that call dma_alloc_coherent(.. GFP_KERNEL) directly can get > unexpected failures. > > Until we have the mask allocator, use a new flag __GFP_NO_OOM > instead of __GFP_NORETRY. > But this change increases the chances of a caller getting stuck in the page allocator for ever, unable to make progress? -- 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