From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with SMTP id 245399000C1 for ; Tue, 26 Apr 2011 07:33:52 -0400 (EDT) Subject: Re: [PATCH 02/13] mm: sl[au]b: Add knowledge of PFMEMALLOC reserve pages From: Mel Gorman In-Reply-To: <20110426211500.02d6a5a6@notabene.brown> References: <1303803414-5937-1-git-send-email-mgorman@suse.de> <1303803414-5937-3-git-send-email-mgorman@suse.de> <20110426211500.02d6a5a6@notabene.brown> Content-Type: text/plain; charset="ISO-8859-15" Date: Tue, 26 Apr 2011 12:33:48 +0100 Message-ID: <1303817628.5593.6.camel@machina.109elm.lan> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: NeilBrown Cc: Linux-MM , Linux-Netdev , LKML , David Miller , Peter Zijlstra On Tue, 2011-04-26 at 21:15 +1000, NeilBrown wrote: > On Tue, 26 Apr 2011 08:36:43 +0100 Mel Gorman wrote: > > > +bool gfp_pfmemalloc_allowed(gfp_t gfp_mask) > > +{ > > + return gfp_to_alloc_flags(gfp_mask) & ALLOC_PFMEMALLOC; > > +} > > + > > static inline struct page * > > __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, > > struct zonelist *zonelist, enum zone_type high_zoneidx, > > @@ -2202,8 +2211,16 @@ nopage: > > got_pg: > > if (kmemcheck_enabled) > > kmemcheck_pagealloc_alloc(page, order, gfp_mask); > > - return page; > > > > + /* > > + * page->pfmemalloc is set when the caller had PFMEMALLOC set or is > > + * been OOM killed. The expectation is that the caller is taking > > + * steps that will free more memory. The caller should avoid the > > + * page being used for !PFMEMALLOC purposes. > > + */ > > + page->pfmemalloc = (alloc_flags & ALLOC_PFMEMALLOC); > > + > > + return page; > > Linus doesn't seem to be a fan of this construct: > https://lkml.org/lkml/2011/4/1/255 > There is confusion around this topic. Andrew prefers bool for true/false values and it's self-documenting. I tend to prefer it myself for readability and there is a slow conversion in the VM from ints-used-as-bools to bools and my understanding of bool is that any non-zero value will be treated as true (just as it is for int). > pfmemalloc is a bool, and the value on the right is either 0 or 0x1000. > > If bool happens to be typedefed to 'char' or even 'short', pfmemalloc would > always be set to 0. It is typedeffed as _Bool though which I thought was able to handle the cast appropriately or is that wrong? > Ditto for the gfp_pfmemalloc_allowed function. > > Prefixing with '!!' would make it safe. > Will do that to avoid any oddities. Thanks -- Mel Gorman SUSE Labs -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org