From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from edge01.upc.biz ([192.168.13.236]) by viefep12-int.chello.at (InterMail vM.7.08.02.00 201-2186-121-20061213) with ESMTP id <20080812081218.MVBZ25075.viefep12-int.chello.at@edge01.upc.biz> for ; Tue, 12 Aug 2008 10:12:18 +0200 Subject: Re: [PATCH 12/30] mm: memory reserve management From: Peter Zijlstra In-Reply-To: <18593.16326.701825.625469@notabene.brown> References: <20080724140042.408642539@chello.nl> <20080724141530.127530749@chello.nl> <18593.16326.701825.625469@notabene.brown> Content-Type: text/plain Date: Tue, 12 Aug 2008 10:12:20 +0200 Message-Id: <1218528740.10800.176.camel@twins> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Neil Brown Cc: Linus Torvalds , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, netdev@vger.kernel.org, trond.myklebust@fys.uio.no, Daniel Lezcano , Pekka Enberg List-ID: On Tue, 2008-08-12 at 17:46 +1000, Neil Brown wrote: > On Thursday July 24, a.p.zijlstra@chello.nl wrote: > > Generic reserve management code. > > > > It provides methods to reserve and charge. Upon this, generic alloc/free style > > reserve pools could be build, which could fully replace mempool_t > > functionality. > > More comments on this patch ..... > > > +void *___kmalloc_reserve(size_t size, gfp_t flags, int node, void *ip, > > + struct mem_reserve *res, int *emerg); > > + > > +static inline > > +void *__kmalloc_reserve(size_t size, gfp_t flags, int node, void *ip, > > + struct mem_reserve *res, int *emerg) > > +{ > > + void *obj; > > + > > + obj = __kmalloc_node_track_caller(size, > > + flags | __GFP_NOMEMALLOC | __GFP_NOWARN, node, ip); > > + if (!obj) > > + obj = ___kmalloc_reserve(size, flags, node, ip, res, emerg); > > + > > + return obj; > > +} > > + > > +#define kmalloc_reserve(size, gfp, node, res, emerg) \ > > + __kmalloc_reserve(size, gfp, node, \ > > + __builtin_return_address(0), res, emerg) > > + > ...... > > +/* > > + * alloc wrappers > > + */ > > + > > +void *___kmalloc_reserve(size_t size, gfp_t flags, int node, void *ip, > > + struct mem_reserve *res, int *emerg) > > +{ > > + void *obj; > > + gfp_t gfp; > > + > > + gfp = flags | __GFP_NOMEMALLOC | __GFP_NOWARN; > > + obj = __kmalloc_node_track_caller(size, gfp, node, ip); > > + > > + if (obj || !(gfp_to_alloc_flags(flags) & ALLOC_NO_WATERMARKS)) > > + goto out; > > + > > + if (res && !mem_reserve_kmalloc_charge(res, size)) { > > + if (!(flags & __GFP_WAIT)) > > + goto out; > > + > > + wait_event(res->waitqueue, > > + mem_reserve_kmalloc_charge(res, size)); > > + > > + obj = __kmalloc_node_track_caller(size, gfp, node, ip); > > + if (obj) { > > + mem_reserve_kmalloc_charge(res, -size); > > + goto out; > > + } > > + } > > + > > + obj = __kmalloc_node_track_caller(size, flags, node, ip); > > + WARN_ON(!obj); > > + if (emerg) > > + *emerg |= 1; > > + > > +out: > > + return obj; > > +} > > Two comments to be precise. > > 1/ __kmalloc_reserve attempts a __GFP_NOMEMALLOC allocation, and then > if that fails, ___kmalloc_reserve immediately tries again. > Is that pointless? Should the second one be removed? Pretty pointless yes, except that it made ___kmalloc_reserve a nicer function to read, and as its an utter slow path I couldn't be arsed to optimize :-) > 2/ mem_reserve_kmalloc_charge appears to assume that the 'mem_reserve' > has been 'connected' and so is active. Hmm, that would be __mem_reserve_charge() then, because the callers don't do much. > While callers probably only set GFP_MEMALLOC in cases where the > mem_reserve is connected, ALLOC_NO_WATERMARKS could get via > PF_MEMALLOC so we could end up calling mem_reserve_kmalloc_charge > when the mem_reserve is not connected. Right.. > That seems to be 'odd' at least. > It might even be 'wrong' as mem_reserve_connect doesn't add the > usage of the child to the parent - only the ->pages and ->limit. > > What is your position on this? Mine is "still slightly confused". Uhmm,. good point. Let me ponder this while I go for breakfast ;-) -- 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