From mboxrd@z Thu Jan 1 00:00:00 1970 Received: by uproxy.gmail.com with SMTP id k40so105002ugc for ; Fri, 27 Jan 2006 03:07:54 -0800 (PST) Message-ID: <84144f020601270307t7266a4ccs5071d4b288a9257f@mail.gmail.com> Date: Fri, 27 Jan 2006 13:07:54 +0200 From: Pekka Enberg Subject: Re: [patch 0/9] Critical Mempools In-Reply-To: <20060127021050.f50d358d.pj@sgi.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Content-Disposition: inline References: <1138217992.2092.0.camel@localhost.localdomain> <43D954D8.2050305@us.ibm.com> <43D95BFE.4010705@us.ibm.com> <20060127000304.GG10409@kvack.org> <43D968E4.5020300@us.ibm.com> <84144f020601262335g49c21b62qaa729732e9275c0@mail.gmail.com> <20060127021050.f50d358d.pj@sgi.com> Sender: owner-linux-mm@kvack.org Return-Path: To: Paul Jackson Cc: colpatch@us.ibm.com, bcrl@kvack.org, clameter@engr.sgi.com, linux-kernel@vger.kernel.org, sri@us.ibm.com, andrea@suse.de, pavel@suse.cz, linux-mm@kvack.org List-ID: Hi, Pekka wrote: > > As as side note, we already have __GFP_NOFAIL. How is it different > > from GFP_CRITICAL and why aren't we improving that? On 1/27/06, Paul Jackson wrote: > Don't these two flags invoke two different mechanisms. > __GFP_NOFAIL can sleep for HZ/50 then retry, rather than return failure. > __GFP_CRITICAL can steal from the emergency pool rather than fail. > > I would favor renaming at least the __GFP_CRITICAL to something > like __GFP_EMERGPOOL, to highlight the relevant distinction. Yeah you're right. __GFP_NOFAIL guarantees to never fail but it doesn't guarantee to actually succeed either. I think the suggested semantics for __GFP_EMERGPOOL are that while it can fail, it tries to avoid that by dipping into page reserves. However, I do still think it's a bad idea to allow the slab allocator to steal whole pages for critical allocations because in low-memory condition, it should be fairly easy to exhaust the reserves and waste most of that memory at the same time. Pekka -- 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