From: Michal Hocko Subject: Re: [PATCH 3/8] mm: introduce memalloc_nofs_{save,restore} API Date: Mon, 9 Jan 2017 14:42:10 +0100 Message-ID: <20170109134210.GI7495@dhcp22.suse.cz> References: <20170106141107.23953-1-mhocko@kernel.org> <20170106141107.23953-4-mhocko@kernel.org> <86dbce74-a532-2f98-6a63-4dbad77b2aa1@suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Andrew Morton , Dave Chinner , djwong@kernel.org, Theodore Ts'o , Chris Mason , David Sterba , Jan Kara , ceph-devel@vger.kernel.org, cluster-devel@redhat.com, linux-nfs@vger.kernel.org, logfs@logfs.org, linux-xfs@vger.kernel.org, linux-ext4@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-mtd@lists.infradead.org, reiserfs-devel@vger.kernel.org, linux-ntfs-dev@lists.sourceforge.net, linux-f2fs-devel@lists.sourceforge.net, linux-afs@lists.infradead.org, LKML To: Vlastimil Babka Return-path: Content-Disposition: inline In-Reply-To: <86dbce74-a532-2f98-6a63-4dbad77b2aa1@suse.cz> Sender: owner-linux-mm@kvack.org List-Id: linux-ext4.vger.kernel.org On Mon 09-01-17 14:04:21, Vlastimil Babka wrote: [...] > > +static inline unsigned int memalloc_nofs_save(void) > > +{ > > + unsigned int flags = current->flags & PF_MEMALLOC_NOFS; > > + current->flags |= PF_MEMALLOC_NOFS; > > So this is not new, as same goes for memalloc_noio_save, but I've > noticed that e.g. exit_signal() does tsk->flags |= PF_EXITING; > So is it possible that there's a r-m-w hazard here? exit_signals operates on current and all task_struct::flags should be used only on the current. [...] > > @@ -3029,7 +3029,7 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg, > > int nid; > > struct scan_control sc = { > > .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX), > > - .gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) | > > + .gfp_mask = (current_gfp_context(gfp_mask) & GFP_RECLAIM_MASK) | > > So this function didn't do memalloc_noio_flags() before? Is it a bug > that should be fixed separately or at least mentioned? Because that > looks like a functional change... We didn't need it. Kmem charges are opt-in and current all of them support GFP_IO. The LRU pages are not charged in NOIO context either. We need it now because there will be callers to charge GFP_KERNEL while being inside the NOFS scope. Now that you have opened this I have noticed that the code is wrong here because GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK would overwrite the removed GFP_FS. I guess it would be better and less error prone to move the current_gfp_context part into the direct reclaim entry - do_try_to_free_pages - and put the comment like this --- diff --git a/mm/vmscan.c b/mm/vmscan.c index 4ea6b610f20e..df7975185f11 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2756,6 +2756,13 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist, int initial_priority = sc->priority; unsigned long total_scanned = 0; unsigned long writeback_threshold; + + /* + * Make sure that the gfp context properly handles scope gfp mask. + * This might weaken the reclaim context (e.g. make it GFP_NOFS or + * GFP_NOIO). + */ + sc->gfp_mask = current_gfp_context(sc->gfp_mask); retry: delayacct_freepages_start(); @@ -2949,7 +2956,7 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order, unsigned long nr_reclaimed; struct scan_control sc = { .nr_to_reclaim = SWAP_CLUSTER_MAX, - .gfp_mask = (gfp_mask = current_gfp_context(gfp_mask)), + .gfp_mask = gfp_mask, .reclaim_idx = gfp_zone(gfp_mask), .order = order, .nodemask = nodemask, @@ -3029,8 +3036,7 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg, int nid; struct scan_control sc = { .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX), - .gfp_mask = (current_gfp_context(gfp_mask) & GFP_RECLAIM_MASK) | - (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK), + .gfp_mask = GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK, .reclaim_idx = MAX_NR_ZONES - 1, .target_mem_cgroup = memcg, .priority = DEF_PRIORITY, @@ -3723,7 +3729,7 @@ static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned in int classzone_idx = gfp_zone(gfp_mask); struct scan_control sc = { .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX), - .gfp_mask = (gfp_mask = current_gfp_context(gfp_mask)), + .gfp_mask = gfp_mask, .order = order, .priority = NODE_RECLAIM_PRIORITY, .may_writepage = !!(node_reclaim_mode & RECLAIM_WRITE), -- Michal Hocko 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/ . Don't email: email@kvack.org