From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, UNPARSEABLE_RELAY,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 049D3C35247 for ; Tue, 4 Feb 2020 23:27:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BBD092087E for ; Tue, 4 Feb 2020 23:27:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727644AbgBDX1c (ORCPT ); Tue, 4 Feb 2020 18:27:32 -0500 Received: from out4436.biz.mail.alibaba.com ([47.88.44.36]:57234 "EHLO out4436.biz.mail.alibaba.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727461AbgBDX1b (ORCPT ); Tue, 4 Feb 2020 18:27:31 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R171e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01f04397;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=6;SR=0;TI=SMTPD_---0TpA9xN9_1580858847; Received: from US-143344MP.local(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0TpA9xN9_1580858847) by smtp.aliyun-inc.com(127.0.0.1); Wed, 05 Feb 2020 07:27:29 +0800 Subject: Re: [v2 PATCH] mm: shmem: allow split THP when truncating THP partially From: Yang Shi To: Hugh Dickins Cc: kirill.shutemov@linux.intel.com, aarcange@redhat.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1575420174-19171-1-git-send-email-yang.shi@linux.alibaba.com> <00f0bb7d-3c25-a65f-ea94-3e2de8e9bcdd@linux.alibaba.com> Message-ID: <33768a7e-837d-3bcd-fb98-19727921d6fd@linux.alibaba.com> Date: Tue, 4 Feb 2020 15:27:25 -0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <00f0bb7d-3c25-a65f-ea94-3e2de8e9bcdd@linux.alibaba.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/14/20 11:28 AM, Yang Shi wrote: > > > On 12/4/19 4:15 PM, Hugh Dickins wrote: >> On Wed, 4 Dec 2019, Yang Shi wrote: >> >>> Currently when truncating shmem file, if the range is partial of THP >>> (start or end is in the middle of THP), the pages actually will just >>> get >>> cleared rather than being freed unless the range cover the whole THP. >>> Even though all the subpages are truncated (randomly or sequentially), >>> the THP may still be kept in page cache.  This might be fine for some >>> usecases which prefer preserving THP. >>> >>> But, when doing balloon inflation in QEMU, QEMU actually does hole >>> punch >>> or MADV_DONTNEED in base page size granulairty if hugetlbfs is not >>> used. >>> So, when using shmem THP as memory backend QEMU inflation actually >>> doesn't >>> work as expected since it doesn't free memory.  But, the inflation >>> usecase really needs get the memory freed.  Anonymous THP will not get >>> freed right away too but it will be freed eventually when all >>> subpages are >>> unmapped, but shmem THP would still stay in page cache. >>> >>> Split THP right away when doing partial hole punch, and if split fails >>> just clear the page so that read to the hole punched area would return >>> zero. >>> >>> Cc: Hugh Dickins >>> Cc: Kirill A. Shutemov >>> Cc: Andrea Arcangeli >>> Signed-off-by: Yang Shi >>> --- >>> v2: * Adopted the comment from Kirill. >>>      * Dropped fallocate mode flag, THP split is the default behavior. >>>      * Blended Huge's implementation with my v1 patch. TBH I'm not >>> very keen to >>>        Hugh's find_get_entries() hack (basically neutral), but >>> without that hack >> Thanks for giving it a try.  I'm not neutral about my find_get_entries() >> hack: it surely had to go (without it, I'd have just pushed my own >> patch). >> I've not noticed anything wrong with your patch, and it's in the right >> direction, but I'm still not thrilled with it.  I also remember that I >> got the looping wrong in my first internal attempt (fixed in what I >> sent), >> and need to be very sure of the try-again-versus-move-on-to-next >> conditions >> before agreeing to anything.  No rush, I'll come back to this in days or >> month ahead: I'll try to find a less gotoey blend of yours and mine. > > Hi Hugh, > > Any update on this one? > > Thanks, > Yang Hi Hugh, Ping. Any comment on this? I really hope it can make v5.7. Thanks, Yang > >> >> Hugh >> >>>        we have to rely on pagevec_release() to release extra pins >>> and play with >>>        goto. This version does in this way. The patch is bigger than >>> Hugh's due >>>        to extra comments to make the flow clear. >>> >>>   mm/shmem.c | 120 >>> ++++++++++++++++++++++++++++++++++++++++++------------------- >>>   1 file changed, 83 insertions(+), 37 deletions(-) >>> >>> diff --git a/mm/shmem.c b/mm/shmem.c >>> index 220be9f..1ae0c7f 100644 >>> --- a/mm/shmem.c >>> +++ b/mm/shmem.c >>> @@ -806,12 +806,15 @@ static void shmem_undo_range(struct inode >>> *inode, loff_t lstart, loff_t lend, >>>       long nr_swaps_freed = 0; >>>       pgoff_t index; >>>       int i; >>> +    bool split = false; >>> +    struct page *page = NULL; >>>         if (lend == -1) >>>           end = -1;    /* unsigned, so actually very big */ >>>         pagevec_init(&pvec); >>>       index = start; >>> +retry: >>>       while (index < end) { >>>           pvec.nr = find_get_entries(mapping, index, >>>               min(end - index, (pgoff_t)PAGEVEC_SIZE), >>> @@ -819,7 +822,8 @@ static void shmem_undo_range(struct inode >>> *inode, loff_t lstart, loff_t lend, >>>           if (!pvec.nr) >>>               break; >>>           for (i = 0; i < pagevec_count(&pvec); i++) { >>> -            struct page *page = pvec.pages[i]; >>> +            split = false; >>> +            page = pvec.pages[i]; >>>                 index = indices[i]; >>>               if (index >= end) >>> @@ -838,23 +842,24 @@ static void shmem_undo_range(struct inode >>> *inode, loff_t lstart, loff_t lend, >>>               if (!trylock_page(page)) >>>                   continue; >>>   -            if (PageTransTail(page)) { >>> -                /* Middle of THP: zero out the page */ >>> -                clear_highpage(page); >>> -                unlock_page(page); >>> -                continue; >>> -            } else if (PageTransHuge(page)) { >>> -                if (index == round_down(end, HPAGE_PMD_NR)) { >>> +            if (PageTransCompound(page) && !unfalloc) { >>> +                if (PageHead(page) && >>> +                    index != round_down(end, HPAGE_PMD_NR)) { >>>                       /* >>> -                     * Range ends in the middle of THP: >>> -                     * zero out the page >>> +                     * Fall through when punching whole >>> +                     * THP. >>>                        */ >>> -                    clear_highpage(page); >>> -                    unlock_page(page); >>> -                    continue; >>> +                    index += HPAGE_PMD_NR - 1; >>> +                    i += HPAGE_PMD_NR - 1; >>> +                } else { >>> +                    /* >>> +                     * Split THP for any partial hole >>> +                     * punch. >>> +                     */ >>> +                    get_page(page); >>> +                    split = true; >>> +                    goto split; >>>                   } >>> -                index += HPAGE_PMD_NR - 1; >>> -                i += HPAGE_PMD_NR - 1; >>>               } >>>                 if (!unfalloc || !PageUptodate(page)) { >>> @@ -866,9 +871,29 @@ static void shmem_undo_range(struct inode >>> *inode, loff_t lstart, loff_t lend, >>>               } >>>               unlock_page(page); >>>           } >>> +split: >>>           pagevec_remove_exceptionals(&pvec); >>>           pagevec_release(&pvec); >>>           cond_resched(); >>> + >>> +        if (split) { >>> +            /* >>> +             * The pagevec_release() released all extra pins >>> +             * from pagevec lookup.  And we hold an extra pin >>> +             * and still have the page locked under us. >>> +             */ >>> +            if (!split_huge_page(page)) { >>> +                unlock_page(page); >>> +                put_page(page); >>> +                /* Re-lookup page cache from current index */ >>> +                goto retry; >>> +            } >>> + >>> +            /* Fail to split THP, move to next index */ >>> +            unlock_page(page); >>> +            put_page(page); >>> +        } >>> + >>>           index++; >>>       } >>>   @@ -901,6 +926,7 @@ static void shmem_undo_range(struct inode >>> *inode, loff_t lstart, loff_t lend, >>>           return; >>>         index = start; >>> +again: >>>       while (index < end) { >>>           cond_resched(); >>>   @@ -916,7 +942,8 @@ static void shmem_undo_range(struct inode >>> *inode, loff_t lstart, loff_t lend, >>>               continue; >>>           } >>>           for (i = 0; i < pagevec_count(&pvec); i++) { >>> -            struct page *page = pvec.pages[i]; >>> +            split = false; >>> +            page = pvec.pages[i]; >>>                 index = indices[i]; >>>               if (index >= end) >>> @@ -936,30 +963,24 @@ static void shmem_undo_range(struct inode >>> *inode, loff_t lstart, loff_t lend, >>>                 lock_page(page); >>>   -            if (PageTransTail(page)) { >>> -                /* Middle of THP: zero out the page */ >>> -                clear_highpage(page); >>> -                unlock_page(page); >>> -                /* >>> -                 * Partial thp truncate due 'start' in middle >>> -                 * of THP: don't need to look on these pages >>> -                 * again on !pvec.nr restart. >>> -                 */ >>> -                if (index != round_down(end, HPAGE_PMD_NR)) >>> -                    start++; >>> -                continue; >>> -            } else if (PageTransHuge(page)) { >>> -                if (index == round_down(end, HPAGE_PMD_NR)) { >>> +            if (PageTransCompound(page) && !unfalloc) { >>> +                if (PageHead(page) && >>> +                    index != round_down(end, HPAGE_PMD_NR)) { >>>                       /* >>> -                     * Range ends in the middle of THP: >>> -                     * zero out the page >>> +                     * Fall through when punching whole >>> +                     * THP. >>>                        */ >>> -                    clear_highpage(page); >>> -                    unlock_page(page); >>> -                    continue; >>> +                    index += HPAGE_PMD_NR - 1; >>> +                    i += HPAGE_PMD_NR - 1; >>> +                } else { >>> +                    /* >>> +                     * Split THP for any partial hole >>> +                     * punch. >>> +                     */ >>> +                    get_page(page); >>> +                    split = true; >>> +                    goto rescan_split; >>>                   } >>> -                index += HPAGE_PMD_NR - 1; >>> -                i += HPAGE_PMD_NR - 1; >>>               } >>>                 if (!unfalloc || !PageUptodate(page)) { >>> @@ -976,8 +997,33 @@ static void shmem_undo_range(struct inode >>> *inode, loff_t lstart, loff_t lend, >>>               } >>>               unlock_page(page); >>>           } >>> +rescan_split: >>>           pagevec_remove_exceptionals(&pvec); >>>           pagevec_release(&pvec); >>> + >>> +        if (split) { >>> +            /* >>> +             * The pagevec_release() released all extra pins >>> +             * from pagevec lookup.  And we hold an extra pin >>> +             * and still have the page locked under us. >>> +             */ >>> +            if (!split_huge_page(page)) { >>> +                unlock_page(page); >>> +                put_page(page); >>> +                /* Re-lookup page cache from current index */ >>> +                goto again; >>> +            } >>> + >>> +            /* >>> +             * Split fail, clear the page then move to next >>> +             * index. >>> +             */ >>> +            clear_highpage(page); >>> + >>> +            unlock_page(page); >>> +            put_page(page); >>> +        } >>> + >>>           index++; >>>       } >>>   -- >>> 1.8.3.1 >>> >>> >