From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f69.google.com (mail-wm0-f69.google.com [74.125.82.69]) by kanga.kvack.org (Postfix) with ESMTP id D94E76B0260 for ; Mon, 9 Oct 2017 00:08:27 -0400 (EDT) Received: by mail-wm0-f69.google.com with SMTP id q203so23660121wmb.0 for ; Sun, 08 Oct 2017 21:08:27 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id v10sor3834301edf.47.2017.10.08.21.08.26 for (Google Transport Security); Sun, 08 Oct 2017 21:08:26 -0700 (PDT) Date: Mon, 9 Oct 2017 07:03:08 +0300 From: "Kirill A. Shutemov" Subject: Re: [RFC PATCH] mm: shm: round up tmpfs size to huge page size when huge=always Message-ID: <20171009040308.qz6ufjrfvyv2hygm@node.shutemov.name> References: <1507321330-22525-1-git-send-email-yang.s@alibaba-inc.com> <20171008125651.3mxiayuvuqi2hiku@node.shutemov.name> <9357e3f2-6e49-b47a-20a6-ec7791c28fbd@alibaba-inc.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <9357e3f2-6e49-b47a-20a6-ec7791c28fbd@alibaba-inc.com> Sender: owner-linux-mm@kvack.org List-ID: To: Yang Shi Cc: kirill.shutemov@linux.intel.com, hughd@google.com, mhocko@kernel.org, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org On Mon, Oct 09, 2017 at 03:51:06AM +0800, Yang Shi wrote: > > > On 10/8/17 5:56 AM, Kirill A. Shutemov wrote: > > On Sat, Oct 07, 2017 at 04:22:10AM +0800, Yang Shi wrote: > > > When passing "huge=always" option for mounting tmpfs, THP is supposed to > > > be allocated all the time when it can fit, but when the available space is > > > smaller than the size of THP (2MB on x86), shmem fault handler still tries > > > to allocate huge page every time, then fallback to regular 4K page > > > allocation, i.e.: > > > > > > # mount -t tmpfs -o huge,size=3000k tmpfs /tmp > > > # dd if=/dev/zero of=/tmp/test bs=1k count=2048 > > > # dd if=/dev/zero of=/tmp/test1 bs=1k count=2048 > > > > > > The last dd command will handle 952 times page fault handler, then exit > > > with -ENOSPC. > > > > > > Rounding up tmpfs size to THP size in order to use THP with "always" > > > more efficiently. And, it will not wast too much memory (just allocate > > > 511 extra pages in worst case). > > > > Hm. I don't think it's good idea to silently increase size of fs. > > How about printing a warning to say the filesystem is resized? > > > > > Maybe better just refuse to mount with huge=always for too small fs? > > It sounds fine too. When mounting tmpfs with "huge=always", if the size is > not THP size aligned, it just can refuse to mount, then show warning about > alignment restriction. Honestly, I wouldn't bother. Using filesystem at near-full capacity is not best practice. Performance penalty for doing is fair enough. And forcing alignment doesn't really fixes anything: user still allowed to fill the filesystem with files less than 2M in size. -- Kirill A. Shutemov -- 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