From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with SMTP id EA02A6B0069 for ; Tue, 22 Nov 2011 00:51:05 -0500 (EST) Message-ID: <4ECB3839.50908@redhat.com> Date: Tue, 22 Nov 2011 13:50:49 +0800 From: Cong Wang MIME-Version: 1.0 Subject: Re: [V2 PATCH] tmpfs: add fallocate support References: <1321612791-4764-1-git-send-email-amwang@redhat.com> <20111119100326.GA27967@infradead.org> <20111121101059.GB17887@infradead.org> In-Reply-To: <20111121101059.GB17887@infradead.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: Christoph Hellwig Cc: Hugh Dickins , Kay Sievers , linux-kernel@vger.kernel.org, akpm@linux-foundation.org, Pekka Enberg , Dave Hansen , Lennart Poettering , KOSAKI Motohiro , linux-mm@kvack.org ao? 2011a1'11ae??21ae?JPY 18:11, Christoph Hellwig a??e??: > On Sun, Nov 20, 2011 at 01:39:12PM -0800, Hugh Dickins wrote: >>> To be able to safely use mmap(), regarding SIGBUS, on files on the >>> /dev/shm filesystem. The glibc fallback loop for -ENOSYS on fallocate >>> is just ugly. >> >> The fallback for -EOPNOTSUPP? > > Probably for both. Note that the fallocate man page actually documents > the errors incorrecly - it documents ENOSYS for filesystems not > supporting fallocate, and EOPNOTSUPP for not recognizing the mode, but > we actually return EOPNOTSUPP for either case. ENOSYS is only returned > by kernels not implementing fallocate at all. We need to fix man page of fallocate(2)... > >> Being unfamiliar with glibc, I failed to find the internal_fallocate() >> that it appears to use when the filesystem doesn't support the call; >> so I don't know if I would agree with you that it's uglier than doing >> the same(?) in the kernel. > > Last time I looked it basically did a pwrite loop writing zeroes. > Unfortunately it did far too small I/O sizes and thus actually causes > some major overhead e.g. on ext3. > >> But since the present situation is that tmpfs has one interface to >> punching holes, madvise(MADV_REMOVE), that IBM were pushing 5 years ago; >> but ext4 (and others) now a fallocate(FALLOC_FL_PUNCH_HOLE) interface >> which IBM have been pushing this year: we do want to normalize that >> situation and make them all behave the same way. > > FALLOC_FL_PUNCH_HOLE was added by Josef Bacik, who happens to work for > Red Hat, but I doubt he was pushing any corporate agenda there, he was > mostly making btrfs catch up with the 15 year old XFS hole punching > ioctl. I sent a patch to util-linux-ng too, http://thread.gmane.org/gmane.linux.utilities.util-linux-ng/5045 > > >> And if tmpfs is going to support fallocate(FALLOC_FL_PUNCH_HOLE), >> looking at Amerigo's much more attractive V2 patch, it would seem >> to me perverse to permit the deallocation but fail the allocation. > > Agreed. > Thanks. -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org