From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx200.postini.com [74.125.245.200]) by kanga.kvack.org (Postfix) with SMTP id AE7516B0044 for ; Tue, 6 Nov 2012 23:35:16 -0500 (EST) Received: from mail-ee0-f41.google.com ([74.125.83.41]) by youngberry.canonical.com with esmtpsa (TLS1.0:RSA_ARCFOUR_SHA1:16) (Exim 4.71) (envelope-from ) id 1TVxMB-0005SU-Ml for linux-mm@kvack.org; Wed, 07 Nov 2012 04:35:15 +0000 Received: by mail-ee0-f41.google.com with SMTP id c4so814598eek.14 for ; Tue, 06 Nov 2012 20:35:15 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20121106194859.8eec3043.akpm@linux-foundation.org> References: <1351931714-11689-1-git-send-email-ming.lei@canonical.com> <1351931714-11689-2-git-send-email-ming.lei@canonical.com> <20121106152354.90150a3b.akpm@linux-foundation.org> <20121106194859.8eec3043.akpm@linux-foundation.org> Date: Wed, 7 Nov 2012 12:35:15 +0800 Message-ID: Subject: Re: [PATCH v4 1/6] mm: teach mm by current context info to not do I/O during memory allocation From: Ming Lei Content-Type: text/plain; charset=ISO-8859-1 Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: linux-kernel@vger.kernel.org, Alan Stern , Oliver Neukum , Minchan Kim , Greg Kroah-Hartman , "Rafael J. Wysocki" , Jens Axboe , "David S. Miller" , netdev@vger.kernel.org, linux-usb@vger.kernel.org, linux-pm@vger.kernel.org, linux-mm@kvack.org, Jiri Kosina , Mel Gorman , KAMEZAWA Hiroyuki , Michal Hocko , Ingo Molnar , Peter Zijlstra On Wed, Nov 7, 2012 at 11:48 AM, Andrew Morton wrote: >> >> Firstly, the patch follows the policy in the system suspend/resume situation, >> in which the __GFP_FS is cleared, and basically the problem is very similar >> with that in system PM path. > > I suspect that code is wrong. Or at least, suboptimal. > >> Secondly, inside shrink_page_list(), pageout() may be triggered on dirty anon >> page if __GFP_FS is set. > > pageout() should be called if GFP_FS is set or if GFP_IO is set and the > IO is against swap. > > And that's what we want to happen: we want to enter the fs to try to > turn dirty pagecache into clean pagecache without doing IO. If we in > fact enter the device drivers when GFP_IO was not set then that's a bug > which we should fix. OK, I got it, and I'll not clear GFP_FS in -v5. > >> IMO, if performing I/O can be completely avoided when __GFP_FS is set, the >> flag can be kept, otherwise it is better to clear it in the situation. > > yup. > >> > >> > Also, you can probably put the unlikely() inside memalloc_noio() and >> > avoid repeating it at all the callsites. >> > >> > And it might be neater to do: >> > >> > /* >> > * Nice comment goes here >> > */ >> > static inline gfp_t memalloc_noio_flags(gfp_t flags) >> > { >> > if (unlikely(current->flags & PF_MEMALLOC_NOIO)) >> > flags &= ~GFP_IOFS; >> > return flags; >> > } >> >> But without the check in callsites, some local variables will be write >> two times, >> so it is better to not do it. > > I don't see why - we just modify the incoming gfp_t at the start of the > function, then use it. > > It gets a bit tricky with those struct initialisations. Things like > > struct foo bar { > .a = a1, > .b = b1, > }; > > should not be turned into > > struct foo bar { > .a = a1, > }; > > bar.b = b1; > > and we don't want to do > > struct foo bar { }; > > bar.a = a1; > bar.b = b1; > > either, because these are indeed a double-write. But we can do > > struct foo bar { > .flags = (flags = memalloc_noio_flags(flags)), > .b = b1, > }; > > which is a bit arcane but not toooo bad. Have a think about it... Got it, looks memalloc_noio_flags() neater, and I will take it in v5. Thanks, -- Ming Lei -- 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