From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754738AbeDYOtn (ORCPT ); Wed, 25 Apr 2018 10:49:43 -0400 Received: from mail-pg0-f67.google.com ([74.125.83.67]:43662 "EHLO mail-pg0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754562AbeDYOtj (ORCPT ); Wed, 25 Apr 2018 10:49:39 -0400 X-Google-Smtp-Source: AIpwx4/4683gQ2tIwie+yq0I5ByWdACXWo7dxClomf1m8D8HHvJC4JEG7oYunGkzbU0mrMdkEalIYQ== Date: Wed, 25 Apr 2018 17:49:38 +0300 From: "Kirill A. Shutemov" To: Yang Shi Cc: kirill.shutemov@linux.intel.com, hughd@google.com, mhocko@kernel.org, hch@infradead.org, viro@zeniv.linux.org.uk, akpm@linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [RFC v5 PATCH] mm: shmem: make stat.st_blksize return huge page size if THP is on Message-ID: <20180425144938.6mv7idgd2u2cyucu@kshutemo-mobl1> References: <1524665633-83806-1-git-send-email-yang.shi@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1524665633-83806-1-git-send-email-yang.shi@linux.alibaba.com> User-Agent: NeoMutt/20180323 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 25, 2018 at 10:13:53PM +0800, Yang Shi wrote: > Since tmpfs THP was supported in 4.8, hugetlbfs is not the only > filesystem with huge page support anymore. tmpfs can use huge page via > THP when mounting by "huge=" mount option. > > When applications use huge page on hugetlbfs, it just need check the > filesystem magic number, but it is not enough for tmpfs. Make > stat.st_blksize return huge page size if it is mounted by appropriate > "huge=" option to give applications a hint to optimize the behavior with > THP. > > Some applications may not do wisely with THP. For example, QEMU may mmap > file on non huge page aligned hint address with MAP_FIXED, which results > in no pages are PMD mapped even though THP is used. Some applications > may mmap file with non huge page aligned offset. Both behaviors make THP > pointless. > > statfs.f_bsize still returns 4KB for tmpfs since THP could be split, and it > also may fallback to 4KB page silently if there is not enough huge page. > Furthermore, different f_bsize makes max_blocks and free_blocks > calculation harder but without too much benefit. Returning huge page > size via stat.st_blksize sounds good enough. > > Since PUD size huge page for THP has not been supported, now it just > returns HPAGE_PMD_SIZE. > > Signed-off-by: Yang Shi > Cc: "Kirill A. Shutemov" > Cc: Hugh Dickins > Cc: Michal Hocko > Cc: Alexander Viro > Suggested-by: Christoph Hellwig Looks good to me: Acked-by: Kirill A. Shutemov -- Kirill A. Shutemov