From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ot0-f197.google.com (mail-ot0-f197.google.com [74.125.82.197]) by kanga.kvack.org (Postfix) with ESMTP id A24F76B000E for ; Tue, 24 Apr 2018 09:09:09 -0400 (EDT) Received: by mail-ot0-f197.google.com with SMTP id r104-v6so7786618ota.19 for ; Tue, 24 Apr 2018 06:09:09 -0700 (PDT) Received: from out30-133.freemail.mail.aliyun.com (out30-133.freemail.mail.aliyun.com. [115.124.30.133]) by mx.google.com with ESMTPS id 79-v6si4038794oth.71.2018.04.24.06.09.06 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 24 Apr 2018 06:09:08 -0700 (PDT) Subject: Re: [RFC v2 PATCH] mm: shmem: make stat.st_blksize return huge page size if THP is on References: <1524242039-64997-1-git-send-email-yang.shi@linux.alibaba.com> <20180423004748.GP17484@dhcp22.suse.cz> <3c59a1d1-dc66-ae5f-452c-dd0adb047433@linux.alibaba.com> <20180423150435.GS17484@dhcp22.suse.cz> <20180424124312.GZ17484@dhcp22.suse.cz> From: Yang Shi Message-ID: Date: Tue, 24 Apr 2018 07:08:36 -0600 MIME-Version: 1.0 In-Reply-To: <20180424124312.GZ17484@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: kirill.shutemov@linux.intel.com, hughd@google.com, 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 On 4/24/18 6:43 AM, Michal Hocko wrote: > On Mon 23-04-18 21:41:50, Yang Shi wrote: >> >> On 4/23/18 9:04 AM, Michal Hocko wrote: >>> On Sun 22-04-18 21:28:59, Yang Shi wrote: >>>> On 4/22/18 6:47 PM, Michal Hocko wrote: >>> [...] >>>>> will be used on the first aligned address even when the initial/last >>>>> portion of the mapping is not THP aligned. >>>> No, my test shows it is not. And, transhuge_vma_suitable() does check the >>>> virtual address alignment. If it is not huge page size aligned, it will not >>>> set PMD for huge page. >>> It's been quite some time since I've looked at that code but I think you >>> are wrong. It just doesn't make sense to make the THP decision on the >>> VMA alignment much. Kirill, can you clarify please? >> Thanks a lot Michal and Kirill to elaborate how tmpfs THP make pmd map. >> >> I did a quick test, THP will be PMD mapped as long as : >> * hint address is huge page aligned if MAP_FIXED >> Or >> * offset is huge page aligned >> And >> * The size is big enough (>= huge page size) >> >> This test does verify what Kirill said. And, I dig into a little further >> qemu code and did strace, qemu does try to mmap the file to non huge page >> aligned address with MAP_FIXED. > Does it make sense to contact Qemu developers and probably fix this? Yes, I think so. We can submit a bug report to QEMU. >