From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx175.postini.com [74.125.245.175]) by kanga.kvack.org (Postfix) with SMTP id F26F66B0087 for ; Sun, 8 Jul 2012 14:12:37 -0400 (EDT) Date: Sun, 8 Jul 2012 20:12:11 +0200 From: Sebastian Andrzej Siewior Subject: Re: [PATCH 04/16] mm: allow PF_MEMALLOC from softirq context Message-ID: <20120708181211.GE2872@breakpoint.cc> References: <1340375443-22455-1-git-send-email-mgorman@suse.de> <1340375443-22455-5-git-send-email-mgorman@suse.de> <20120626165513.GD6509@breakpoint.cc> <20120627082614.GE8271@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120627082614.GE8271@suse.de> Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: Andrew Morton , Linux-MM , Linux-Netdev , LKML , David Miller , Neil Brown , Peter Zijlstra , Mike Christie , Eric B Munson , Eric Dumazet On Wed, Jun 27, 2012 at 09:26:14AM +0100, Mel Gorman wrote: > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > > index b6c0727..5c6d9c6 100644 > > > --- a/mm/page_alloc.c > > > +++ b/mm/page_alloc.c > > > @@ -2265,7 +2265,11 @@ gfp_to_alloc_flags(gfp_t gfp_mask) > > > if (likely(!(gfp_mask & __GFP_NOMEMALLOC))) { > > > if (gfp_mask & __GFP_MEMALLOC) > > > alloc_flags |= ALLOC_NO_WATERMARKS; > > > - else if (likely(!(gfp_mask & __GFP_NOMEMALLOC)) && !in_interrupt()) > > > + else if (in_serving_softirq() && (current->flags & PF_MEMALLOC)) > > > + alloc_flags |= ALLOC_NO_WATERMARKS; > > > + else if (!in_interrupt() && > > > + ((current->flags & PF_MEMALLOC) || > > > + unlikely(test_thread_flag(TIF_MEMDIE)))) > > > alloc_flags |= ALLOC_NO_WATERMARKS; > > > } > > > > You allocate in RX path with __GFP_MEMALLOC and your sk->sk_allocation has > > also __GFP_MEMALLOC set. That means you should get ALLOC_NO_WATERMARKS in > > alloc_flags. > > In the cases where they are annotated correctly, yes. It is recordeed if > the page gets allocated from the PFMEMALLOC reserves. If the received > packet is not SOCK_MEMALLOC and the page was allocated from PFMEMALLOC > reserves it is then discarded and the packet must be retransmitted. Let me try again: - lets assume your allocation happens with alloc_page(), without __GFP_MEMALLOC in GFP_FLAGS and with PF_MEMALLOC in current->flags. Now you may get memory which you wouldn't receive otherwise (without PF_MEMALLOC). Okay, understood. So you don't have to annotate each page allocation in your receive path for instance as long as the process has the flag set. - lets assume your allocation happens with kmalloc() without __GFP_MEMALLOC and current->flags has PF_MEMALLOC ORed and your SLAB pool is empty. This forces SLAB to allocate more pages from the buddy allocator with it will receive more likely (due to ->current->flags + PF_MEMALLOC) but SLAB will drop this extra memory because the page has ->pf_memory (or something like that) set and the GFP_FLAGS do not have __GFP_MEMALLOC set. Is there something I missed? Sebastian -- 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