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=-9.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, UNPARSEABLE_RELAY,USER_AGENT_GIT autolearn=unavailable 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 39F6CC432C0 for ; Wed, 4 Dec 2019 00:43:17 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 87DB1207DD for ; Wed, 4 Dec 2019 00:43:16 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 87DB1207DD Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 1BF4A6B07C6; Tue, 3 Dec 2019 19:43:16 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 170CF6B07C7; Tue, 3 Dec 2019 19:43:16 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 05EE86B07C8; Tue, 3 Dec 2019 19:43:16 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0165.hostedemail.com [216.40.44.165]) by kanga.kvack.org (Postfix) with ESMTP id E49C06B07C6 for ; Tue, 3 Dec 2019 19:43:15 -0500 (EST) Received: from smtpin07.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with SMTP id 96F97181AC9CB for ; Wed, 4 Dec 2019 00:43:15 +0000 (UTC) X-FDA: 76225609950.07.soup29_1c5c599918c07 X-HE-Tag: soup29_1c5c599918c07 X-Filterd-Recvd-Size: 8195 Received: from out4436.biz.mail.alibaba.com (out4436.biz.mail.alibaba.com [47.88.44.36]) by imf38.hostedemail.com (Postfix) with ESMTP for ; Wed, 4 Dec 2019 00:43:14 +0000 (UTC) X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R181e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04420;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=7;SR=0;TI=SMTPD_---0Tjr3EVU_1575420174; Received: from e19h19392.et15sqa.tbsite.net(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0Tjr3EVU_1575420174) by smtp.aliyun-inc.com(127.0.0.1); Wed, 04 Dec 2019 08:43:01 +0800 From: Yang Shi To: hughd@google.com, kirill.shutemov@linux.intel.com, aarcange@redhat.com, akpm@linux-foundation.org Cc: yang.shi@linux.alibaba.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [v2 PATCH] mm: shmem: allow split THP when truncating THP partially Date: Wed, 4 Dec 2019 08:42:54 +0800 Message-Id: <1575420174-19171-1-git-send-email-yang.shi@linux.alibaba.com> X-Mailer: git-send-email 1.8.3.1 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 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