From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx195.postini.com [74.125.245.195]) by kanga.kvack.org (Postfix) with SMTP id 306A26B005C for ; Wed, 13 Jun 2012 23:53:45 -0400 (EDT) Received: by pbbrp2 with SMTP id rp2so3842319pbb.14 for ; Wed, 13 Jun 2012 20:53:44 -0700 (PDT) Date: Wed, 13 Jun 2012 20:53:42 -0700 (PDT) From: David Rientjes Subject: Re: [PATCH] mm: add gfp_mask parameter to vm_map_ram() In-Reply-To: <20120614033429.GD7339@dastard> Message-ID: References: <20120612012134.GA7706@localhost> <20120613123932.GA1445@localhost> <20120614012026.GL3019@devil.redhat.com> <20120614014902.GB7289@localhost> <4FD94779.3030108@kernel.org> <20120614033429.GD7339@dastard> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Dave Chinner Cc: Minchan Kim , Fengguang Wu , Dave Chinner , Christoph Hellwig , linux-fsdevel@vger.kernel.org, LKML , Andrew Morton , Tejun Heo , Linux Memory Management List , xfs@oss.sgi.com On Thu, 14 Jun 2012, Dave Chinner wrote: > Oh, please. I have been hearing this for years, and are we any > closer to it? No, we are further away from ever being able to > acheive this than ever. Face it, filesystems require memory > allocation to write dirty data to disk, and the amount is almost > impossible to define. Hence mempools can't be used because we can't > give any guarantees of forward progress. And for vmalloc? > > Filesystems widely use vmalloc/vm_map_ram because kmalloc fails on > large contiguous allocations. This renders kmalloc unfit for > purpose, so we have to fall back to single page allocation and > vm_map_ram or vmalloc so that the filesystem can function properly. > And to avoid deadlocks, all memory allocation must be able to > specify GFP_NOFS to prevent the MM subsystem from recursing into the > filesystem. Therefore, vmalloc needs to support GFP_NOFS. > > I don't care how you make it happen, just fix it. Trying to place > the blame on the filesystem folk for using vmalloc in GFP_NOFS > contexts is a total and utter cop-out, because mm folk of all people > should know that non-zero order kmalloc is not a reliable > alternative.... > I'd actually like to see a demonstrated problem (i.e. not theoretical) where vmalloc() stalls indefinitely because its passed GFP_NOFS. I've never seen one reported. This is because the per-arch pte allocators have hardwired GFP_KERNEL flags, but then again they also have __GFP_REPEAT which would cause them to loop infinitely in the page allocator if a page was not reclaimed, which has little success without __GFP_FS. But nobody has ever reported a livelock that was triaged back to passing !__GFP_FS to vmalloc(). -- 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