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[37.188.133.87]) by smtp.gmail.com with ESMTPSA id m9sm5915978wrx.55.2020.02.13.22.55.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 13 Feb 2020 22:55:05 -0800 (PST) Date: Fri, 14 Feb 2020 07:55:04 +0100 From: Michal Hocko To: Matthew Wilcox Cc: Cong Wang , LKML , Andrew Morton , linux-mm , Mel Gorman , Vlastimil Babka Subject: Re: [PATCH] mm: avoid blocking lock_page() in kcompactd Message-ID: <20200214065504.GK31689@dhcp22.suse.cz> References: <20200127190653.GA8708@bombadil.infradead.org> <20200128081712.GA18145@dhcp22.suse.cz> <20200128083044.GB6615@bombadil.infradead.org> <20200128091352.GC18145@dhcp22.suse.cz> <20200128104857.GC6615@bombadil.infradead.org> <20200128113953.GA24244@dhcp22.suse.cz> <20200213074847.GB31689@dhcp22.suse.cz> <20200213164607.GR7778@bombadil.infradead.org> <20200213170824.GJ31689@dhcp22.suse.cz> <20200214042724.GY7778@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200214042724.GY7778@bombadil.infradead.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 13-02-20 20:27:24, Matthew Wilcox wrote: > On Thu, Feb 13, 2020 at 06:08:24PM +0100, Michal Hocko wrote: > > On Thu 13-02-20 08:46:07, Matthew Wilcox wrote: > > > On Thu, Feb 13, 2020 at 08:48:47AM +0100, Michal Hocko wrote: > > > > Can we pursue on this please? An explicit NOFS scope annotation with a > > > > reference to compaction potentially locking up on pages in the readahead > > > > would be a great start. > > > > > > How about this (on top of the current readahead series): > > > > > > diff --git a/mm/readahead.c b/mm/readahead.c > > > index 29ca25c8f01e..32fd32b913da 100644 > > > --- a/mm/readahead.c > > > +++ b/mm/readahead.c > > > @@ -160,6 +160,16 @@ unsigned long page_cache_readahead_limit(struct address_space *mapping, > > > .nr_pages = 0, > > > }; > > > > > > + /* > > > + * Partway through the readahead operation, we will have added > > > + * locked pages to the page cache, but will not yet have submitted > > > + * them for I/O. Adding another page may need to allocate > > > + * memory, which can trigger memory migration. Telling the VM > > > > I would go with s@migration@compaction@ because it would make it more > > obvious that this is about high order allocations. > > Perhaps even just 'reclaim' -- it's about compaction today, but tomorrow's > VM might try to reclaim these pages too. They are on the LRU, after all. > > So I currently have: > > /* > * Partway through the readahead operation, we will have added > * locked pages to the page cache, but will not yet have submitted > * them for I/O. Adding another page may need to allocate memory, > * which can trigger memory reclaim. Telling the VM we're in > * the middle of a filesystem operation will cause it to not > * touch file-backed pages, preventing a deadlock. Most (all?) > * filesystems already specify __GFP_NOFS in their mapping's > * gfp_mask, but let's be explicit here. > */ OK, Thanks! -- Michal Hocko SUSE Labs