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=-10.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,HTML_MESSAGE,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY 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 675CAC433FE for ; Thu, 9 Sep 2021 01:25:59 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id CAE6160234 for ; Thu, 9 Sep 2021 01:25:58 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org CAE6160234 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=kvack.org Received: by kanga.kvack.org (Postfix) id 3F2FF6B0071; Wed, 8 Sep 2021 21:25:58 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 39F2B6B0072; Wed, 8 Sep 2021 21:25:58 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1F2476B0073; Wed, 8 Sep 2021 21:25:58 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0199.hostedemail.com [216.40.44.199]) by kanga.kvack.org (Postfix) with ESMTP id 0A3A16B0071 for ; Wed, 8 Sep 2021 21:25:58 -0400 (EDT) Received: from smtpin34.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 92CF22C5AE for ; Thu, 9 Sep 2021 01:25:57 +0000 (UTC) X-FDA: 78566293554.34.F6C6A96 Received: from out30-54.freemail.mail.aliyun.com (out30-54.freemail.mail.aliyun.com [115.124.30.54]) by imf30.hostedemail.com (Postfix) with ESMTP id 7B8D3E001983 for ; Thu, 9 Sep 2021 01:25:55 +0000 (UTC) X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R131e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=alimailimapcm10staff010182156082;MF=rongwei.wang@linux.alibaba.com;NM=1;PH=DS;RN=9;SR=0;TI=SMTPD_---0UnjjbLw_1631150750; Received: from 30.240.104.109(mailfrom:rongwei.wang@linux.alibaba.com fp:SMTPD_---0UnjjbLw_1631150750) by smtp.aliyun-inc.com(127.0.0.1); Thu, 09 Sep 2021 09:25:51 +0800 From: Rongwei Wang Message-Id: Content-Type: multipart/alternative; boundary="Apple-Mail=_C68AB883-13D5-4815-8775-658F75B14E31" Mime-Version: 1.0 (Mac OS X Mail 14.0 \(3654.60.0.2.21\)) Subject: Re: [PATCH 1/2] mm, thp: check page mapping when truncating page cache Date: Thu, 9 Sep 2021 09:25:49 +0800 In-Reply-To: Cc: Linux MM , Linux Kernel Mailing List , Andrew Morton , cfijalkovich@google.com, song@kernel.org, william.kucharski@oracle.com, Hugh Dickins , Matthew Wilcox To: Yang Shi References: <20210906121200.57905-1-rongwei.wang@linux.alibaba.com> <20210906121200.57905-2-rongwei.wang@linux.alibaba.com> <38AF4DC8-5E6F-4568-B2E3-0434BD847BC9@linux.alibaba.com> X-Mailer: Apple Mail (2.3654.60.0.2.21) X-Stat-Signature: k7y7p9wmwiywanh5werio3zpjw1hnxwe Authentication-Results: imf30.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=alibaba.com; spf=pass (imf30.hostedemail.com: domain of rongwei.wang@linux.alibaba.com designates 115.124.30.54 as permitted sender) smtp.mailfrom=rongwei.wang@linux.alibaba.com X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 7B8D3E001983 X-HE-Tag: 1631150755-108923 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: --Apple-Mail=_C68AB883-13D5-4815-8775-658F75B14E31 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=utf-8 > On Sep 9, 2021, at 5:48 AM, Yang Shi wrote: >=20 > On Tue, Sep 7, 2021 at 7:41 PM Rongwei Wang > > wrote: >>=20 >>=20 >>=20 >> On Sep 8, 2021, at 2:08 AM, Yang Shi wrote: >>=20 >> On Mon, Sep 6, 2021 at 5:12 AM Rongwei Wang >> wrote: >>=20 >>=20 >> Transparent huge page has supported read-only non-shmem files. The = file- >> backed THP is collapsed by khugepaged and truncated when written (for >> shared libraries). >>=20 >> However, there is race in two possible places. >>=20 >> 1) multiple writers truncate the same page cache concurrently; >> 2) collapse_file rolls back when writer truncates the page cache; >>=20 >> In both cases, subpage(s) of file THP can be revealed by = find_get_entry >> in truncate_inode_pages_range, which will trigger PageTail BUG_ON in >> truncate_inode_page, as follows. >>=20 >> [40326.247034] page:000000009e420ff2 refcount:1 mapcount:0 = mapping:0000000000000000 index:0x7ff pfn:0x50c3ff >> [40326.247041] head:0000000075ff816d order:9 compound_mapcount:0 = compound_pincount:0 >> [40326.247046] flags: = 0x37fffe0000010815(locked|uptodate|lru|arch_1|head) >> [40326.247051] raw: 37fffe0000000000 fffffe0013108001 = dead000000000122 dead000000000400 >> [40326.247053] raw: 0000000000000001 0000000000000000 = 00000000ffffffff 0000000000000000 >> [40326.247055] head: 37fffe0000010815 fffffe001066bd48 = ffff000404183c20 0000000000000000 >> [40326.247057] head: 0000000000000600 0000000000000000 = 00000001ffffffff ffff000c0345a000 >> [40326.247058] page dumped because: VM_BUG_ON_PAGE(PageTail(page)) >> [40326.247077] ------------[ cut here ]------------ >> [40326.247080] kernel BUG at mm/truncate.c:213! >> [40326.280581] Internal error: Oops - BUG: 0 [#1] SMP >> [40326.281077] Modules linked in: xfs(E) libcrc32c(E) rfkill(E) = aes_ce_blk(E) crypto_simd(E) cryptd(E) aes_ce_cipher(E) crct10dif_ce(E) = ghash_ce(E) sha1_ce(E) uio_pdrv_genirq(E) uio(E) nfsd(E) vfat(E) fat(E) = auth_rpcgss(E) nfs_acl(E) lockd(E) grace(E) sunrpc(E) sch_fq_codel(E) = ip_tables(E) ext4(E) mbcache(E) jbd2(E) virtio_net(E) net_failover(E) = virtio_blk(E) failover(E) sha2_ce(E) sha256_arm64(E) virtio_mmio(E) = virtio_pci(E) virtio_ring(E) virtio(E) >> [40326.285130] CPU: 14 PID: 11394 Comm: check_madvise_d Kdump: loaded = Tainted: G W E 5.10.46-hugetext+ #55 >> [40326.286202] Hardware name: Alibaba Cloud Alibaba Cloud ECS, BIOS = 0.0.0 02/06/2015 >> [40326.286968] pstate: 60400005 (nZCv daif +PAN -UAO -TCO BTYPE=3D--) >> [40326.287584] pc : truncate_inode_page+0x64/0x70 >> [40326.288040] lr : truncate_inode_page+0x64/0x70 >> [40326.288498] sp : ffff80001b60b900 >> [40326.288837] x29: ffff80001b60b900 x28: 00000000000007ff >> [40326.289377] x27: ffff80001b60b9a0 x26: 0000000000000000 >> [40326.289943] x25: 000000000000000f x24: ffff80001b60b9a0 >> [40326.290485] x23: ffff80001b60ba18 x22: ffff0001e0999ea8 >> [40326.291027] x21: ffff0000c21db300 x20: ffffffffffffffff >> [40326.291566] x19: fffffe001310ffc0 x18: 0000000000000020 >> [40326.292106] x17: 0000000000000000 x16: 0000000000000000 >> [40326.292655] x15: ffff0000c21db960 x14: 3030306666666620 >> [40326.293197] x13: 6666666666666666 x12: 3130303030303030 >> [40326.293746] x11: ffff8000117b69b8 x10: 00000000ffff8000 >> [40326.294313] x9 : ffff80001012690c x8 : 0000000000000000 >> [40326.294851] x7 : ffff8000114f69b8 x6 : 0000000000017ffd >> [40326.295392] x5 : ffff0007fffbcbc8 x4 : ffff80001b60b5c0 >> [40326.295942] x3 : 0000000000000001 x2 : 0000000000000000 >> [40326.296497] x1 : 0000000000000000 x0 : 0000000000000000 >> [40326.297047] Call trace: >> [40326.297304] truncate_inode_page+0x64/0x70 >> [40326.297724] truncate_inode_pages_range+0x550/0x7e4 >> [40326.298251] truncate_pagecache+0x58/0x80 >> [40326.298662] do_dentry_open+0x1e4/0x3c0 >> [40326.299052] vfs_open+0x38/0x44 >> [40326.299377] do_open+0x1f0/0x310 >> [40326.299709] path_openat+0x114/0x1dc >> [40326.300077] do_filp_open+0x84/0x134 >> [40326.300444] do_sys_openat2+0xbc/0x164 >> [40326.300825] __arm64_sys_openat+0x74/0xc0 >> [40326.301236] el0_svc_common.constprop.0+0x88/0x220 >> [40326.301723] do_el0_svc+0x30/0xa0 >> [40326.302089] el0_svc+0x20/0x30 >> [40326.302404] el0_sync_handler+0x1a4/0x1b0 >> [40326.302814] el0_sync+0x180/0x1c0 >> [40326.303157] Code: aa0103e0 900061e1 910ec021 9400d300 (d4210000) >> [40326.303775] ---[ end trace f70cdb42cb7c2d42 ]--- >> [40326.304244] Kernel panic - not syncing: Oops - BUG: Fatal = exception >>=20 >> This checks the page mapping and retries when subpage of file THP is >> found, in truncate_inode_pages_range. >>=20 >> Fixes: eb6ecbed0aa2 ("mm, thp: relax the VM_DENYWRITE constraint on = file-backed THPs") >> Signed-off-by: Xu Yu >> Signed-off-by: Rongwei Wang >> --- >> mm/filemap.c | 7 ++++++- >> mm/truncate.c | 17 ++++++++++++++++- >> 2 files changed, 22 insertions(+), 2 deletions(-) >>=20 >> diff --git a/mm/filemap.c b/mm/filemap.c >> index dae481293..a3af2ec 100644 >> --- a/mm/filemap.c >> +++ b/mm/filemap.c >> @@ -2093,7 +2093,6 @@ unsigned find_lock_entries(struct address_space = *mapping, pgoff_t start, >> if (!xa_is_value(page)) { >> if (page->index < start) >> goto put; >> - VM_BUG_ON_PAGE(page->index !=3D xas.xa_index, = page); >> if (page->index + thp_nr_pages(page) - 1 > end) >> goto put; >> if (!trylock_page(page)) >> @@ -2102,6 +2101,12 @@ unsigned find_lock_entries(struct = address_space *mapping, pgoff_t start, >> goto unlock; >> VM_BUG_ON_PAGE(!thp_contains(page, = xas.xa_index), >> page); >> + /* >> + * We can find and get head page of file THP = with >> + * non-head index. The head page should have = already >> + * be truncated with page->mapping reset to = NULL. >> + */ >> + VM_BUG_ON_PAGE(page->index !=3D xas.xa_index, = page); >> } >> indices[pvec->nr] =3D xas.xa_index; >> if (!pagevec_add(pvec, page)) >> diff --git a/mm/truncate.c b/mm/truncate.c >> index 714eaf1..8c59c00 100644 >> --- a/mm/truncate.c >> +++ b/mm/truncate.c >> @@ -319,7 +319,8 @@ void truncate_inode_pages_range(struct = address_space *mapping, >> index =3D start; >> while (index < end && find_lock_entries(mapping, index, end - = 1, >> &pvec, indices)) { >> - index =3D indices[pagevec_count(&pvec) - 1] + 1; >> + index =3D indices[pagevec_count(&pvec) - 1] + >> + thp_nr_pages(pvec.pages[pagevec_count(&pvec) = - 1]); >>=20 >>=20 >> I don't quite get what this change is doing for. IIUC >> find_lock_entries() already handles index advance correctly. If >> truncate range is partial THP, it will be handled in the second pass. >>=20 >> Yes, agree. >>=20 >> AFAICT, the problem is why the THP is not split if it will get >>=20 >> Yes, agree. >>=20 >> This change is not necessary, but nice to have. Because = find_lock_entries() >> return only head page if any, and it is better to advance the index = by thp_nr_pages(), instead of 1. >>=20 >> If you think it introduces unnecessary complexity, I don't mind = discarding this change. >=20 > IIUC this change may reduce some runtime overhead (-1 call to > find_lock_entries()), but I'd suggest you wait for the comments from > Matthew. OK, I am agree with your suggestion. Thanks! >=20 >>=20 >> partially truncated. Did I miss something? >>=20 >>=20 >>=20 >> truncate_exceptional_pvec_entries(mapping, &pvec, = indices); >> for (i =3D 0; i < pagevec_count(&pvec); i++) >> truncate_cleanup_page(pvec.pages[i]); >> @@ -391,6 +392,20 @@ void truncate_inode_pages_range(struct = address_space *mapping, >> if (xa_is_value(page)) >> continue; >>=20 >> + /* >> + * Already truncated? We can find and get = subpage >> + * of file THP, of which the head page is = truncated. >> + * >> + * In addition, another race will be avoided, = where >> + * collapse_file rolls back when writer = truncates the >> + * page cache. >> + */ >> + if (page_mapping(page) !=3D mapping) { >> + /* Restart to make sure all gone */ >> + index =3D start - 1; >> + continue; >> + } >> + >> lock_page(page); >> WARN_ON(page_to_index(page) !=3D index); >> wait_on_page_writeback(page); >> =E2=80=94 >> 1.8.3.1 >>=20 >> Thanks, >> Rongwei Wang --Apple-Mail=_C68AB883-13D5-4815-8775-658F75B14E31 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=utf-8

On Sep 9, 2021, at 5:48 AM, Yang Shi <shy828301@gmail.com>= wrote:

On Tue, Sep 7, 2021 at 7:41 PM Rongwei Wang
<rongwei.wang@linux.alibaba.com> wrote:



On Sep 8, 2021, at 2:08 AM, Yang Shi <shy828301@gmail.com>= wrote:

On Mon, Sep 6, 2021 at 5:12 AM = Rongwei Wang
<rongwei.wang@linux.alibaba.com> wrote:

Transparent huge page has supported read-only = non-shmem files. The file-
backed THP is collapsed by = khugepaged and truncated when written (for
shared = libraries).

However, there is race in two = possible places.

1) multiple writers = truncate the same page cache concurrently;
2) = collapse_file rolls back when writer truncates the page cache;

In both cases, subpage(s) of file THP can be = revealed by find_get_entry
in truncate_inode_pages_range, = which will trigger PageTail BUG_ON in
truncate_inode_page, = as follows.

[40326.247034] = page:000000009e420ff2 refcount:1 mapcount:0 mapping:0000000000000000 = index:0x7ff pfn:0x50c3ff
[40326.247041] = head:0000000075ff816d order:9 compound_mapcount:0 compound_pincount:0
[40326.247046] flags: = 0x37fffe0000010815(locked|uptodate|lru|arch_1|head)
[40326.247051] raw: 37fffe0000000000 fffffe0013108001 = dead000000000122 dead000000000400
[40326.247053] raw: = 0000000000000001 0000000000000000 00000000ffffffff 0000000000000000
[40326.247055] head: 37fffe0000010815 fffffe001066bd48 = ffff000404183c20 0000000000000000
[40326.247057] head: = 0000000000000600 0000000000000000 00000001ffffffff ffff000c0345a000
[40326.247058] page dumped because: = VM_BUG_ON_PAGE(PageTail(page))
[40326.247077] = ------------[ cut here ]------------
[40326.247080] kernel = BUG at mm/truncate.c:213!
[40326.280581] Internal error: = Oops - BUG: 0 [#1] SMP
[40326.281077] Modules linked in: = xfs(E) libcrc32c(E) rfkill(E) aes_ce_blk(E) crypto_simd(E) cryptd(E) = aes_ce_cipher(E) crct10dif_ce(E) ghash_ce(E) sha1_ce(E) = uio_pdrv_genirq(E) uio(E) nfsd(E) vfat(E) fat(E) auth_rpcgss(E) = nfs_acl(E) lockd(E) grace(E) sunrpc(E) sch_fq_codel(E) ip_tables(E) = ext4(E) mbcache(E) jbd2(E) virtio_net(E) net_failover(E) virtio_blk(E) = failover(E) sha2_ce(E) sha256_arm64(E) virtio_mmio(E) virtio_pci(E) = virtio_ring(E) virtio(E)
[40326.285130] CPU: 14 PID: 11394 = Comm: check_madvise_d Kdump: loaded Tainted: G =        W   E =     5.10.46-hugetext+ #55
[40326.286202]= Hardware name: Alibaba Cloud Alibaba Cloud ECS, BIOS 0.0.0 = 02/06/2015
[40326.286968] pstate: 60400005 (nZCv daif +PAN = -UAO -TCO BTYPE=3D--)
[40326.287584] pc : = truncate_inode_page+0x64/0x70
[40326.288040] lr : = truncate_inode_page+0x64/0x70
[40326.288498] sp : = ffff80001b60b900
[40326.288837] x29: ffff80001b60b900 x28: = 00000000000007ff
[40326.289377] x27: ffff80001b60b9a0 x26: = 0000000000000000
[40326.289943] x25: 000000000000000f x24: = ffff80001b60b9a0
[40326.290485] x23: ffff80001b60ba18 x22: = ffff0001e0999ea8
[40326.291027] x21: ffff0000c21db300 x20: = ffffffffffffffff
[40326.291566] x19: fffffe001310ffc0 x18: = 0000000000000020
[40326.292106] x17: 0000000000000000 x16: = 0000000000000000
[40326.292655] x15: ffff0000c21db960 x14: = 3030306666666620
[40326.293197] x13: 6666666666666666 x12: = 3130303030303030
[40326.293746] x11: ffff8000117b69b8 x10: = 00000000ffff8000
[40326.294313] x9 : ffff80001012690c x8 : = 0000000000000000
[40326.294851] x7 : ffff8000114f69b8 x6 : = 0000000000017ffd
[40326.295392] x5 : ffff0007fffbcbc8 x4 : = ffff80001b60b5c0
[40326.295942] x3 : 0000000000000001 x2 : = 0000000000000000
[40326.296497] x1 : 0000000000000000 x0 : = 0000000000000000
[40326.297047] Call trace:
[40326.297304]  truncate_inode_page+0x64/0x70
[40326.297724] =  truncate_inode_pages_range+0x550/0x7e4
[40326.298251] =  truncate_pagecache+0x58/0x80
[40326.298662] =  do_dentry_open+0x1e4/0x3c0
[40326.299052] =  vfs_open+0x38/0x44
[40326.299377] =  do_open+0x1f0/0x310
[40326.299709] =  path_openat+0x114/0x1dc
[40326.300077] =  do_filp_open+0x84/0x134
[40326.300444] =  do_sys_openat2+0xbc/0x164
[40326.300825] =  __arm64_sys_openat+0x74/0xc0
[40326.301236] =  el0_svc_common.constprop.0+0x88/0x220
[40326.301723] =  do_el0_svc+0x30/0xa0
[40326.302089] =  el0_svc+0x20/0x30
[40326.302404] =  el0_sync_handler+0x1a4/0x1b0
[40326.302814] =  el0_sync+0x180/0x1c0
[40326.303157] Code: aa0103e0 = 900061e1 910ec021 9400d300 (d4210000)
[40326.303775] ---[ = end trace f70cdb42cb7c2d42 ]---
[40326.304244] Kernel = panic - not syncing: Oops - BUG: Fatal exception

This checks the page mapping and retries when subpage of file = THP is
found, in truncate_inode_pages_range.

Fixes: eb6ecbed0aa2 ("mm, thp: relax the = VM_DENYWRITE constraint on file-backed THPs")
Signed-off-by:= Xu Yu <xuyu@linux.alibaba.com>
Signed-off-by: = Rongwei Wang <rongwei.wang@linux.alibaba.com>
---
mm/filemap.c  |  7 ++++++-
mm/truncate.c | 17 ++++++++++++++++-
2 files = changed, 22 insertions(+), 2 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index = dae481293..a3af2ec 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2093,7 +2093,6 @@ = unsigned find_lock_entries(struct address_space *mapping, pgoff_t = start,
          &nb= sp;   if (!xa_is_value(page)) {
          &nb= sp;           if = (page->index < start)
          &nb= sp;            = ;       goto put;
- =             &n= bsp;         VM_BUG_ON_PAGE(p= age->index !=3D xas.xa_index, page);
          &nb= sp;           if = (page->index + thp_nr_pages(page) - 1 > end)
          &nb= sp;            = ;       goto put;
          &nb= sp;           if = (!trylock_page(page))
@@ -2102,6 +2101,12 @@ unsigned = find_lock_entries(struct address_space *mapping, pgoff_t start,
          &nb= sp;            = ;       goto unlock;
          &nb= sp;           VM_BU= G_ON_PAGE(!thp_contains(page, xas.xa_index),
          &nb= sp;            = ;            &= nbsp;  page);
+ =             &n= bsp;         /*
+ =             &n= bsp;          * We can = find and get head page of file THP with
+ =             &n= bsp;          * = non-head index. The head page should have already
+ =             &n= bsp;          * be = truncated with page->mapping reset to NULL.
+ =             &n= bsp;          */
+ =             &n= bsp;         VM_BUG_ON_PAGE(p= age->index !=3D xas.xa_index, page);
          &nb= sp;   }
          &nb= sp;   indices[pvec->nr] =3D xas.xa_index;
          &nb= sp;   if (!pagevec_add(pvec, page))
diff = --git a/mm/truncate.c b/mm/truncate.c
index = 714eaf1..8c59c00 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -319,7 +319,8 @@ void = truncate_inode_pages_range(struct address_space *mapping,
      index =3D start;
      while (index < end = && find_lock_entries(mapping, index, end - 1,
          &nb= sp;           &= pvec, indices)) {
- =             &n= bsp; index =3D indices[pagevec_count(&pvec) - 1] + 1;
+ =             &n= bsp; index =3D indices[pagevec_count(&pvec) - 1] +
+ =             &n= bsp;         thp_nr_pages(pve= c.pages[pagevec_count(&pvec) - 1]);


I don't quite get what this change is doing for. IIUC
find_lock_entries() already handles index advance correctly. = If
truncate range is partial THP, it will be handled in = the second pass.

Yes, agree.

AFAICT, the problem is why the THP is not = split if it will get

Yes, agree.

This change is not necessary, but nice to = have. Because find_lock_entries()
return only head page if = any, and it is better to advance the index by thp_nr_pages(), instead of = 1.

If you think it introduces unnecessary = complexity, I don't mind discarding this change.

IIUC this change may reduce some runtime overhead (-1 call = to
find_lock_entries()), but I'd suggest you wait for the = comments from
Matthew.
OK, I am agree = with your suggestion.

Thanks!


partially truncated. Did I miss something?



          &nb= sp;   truncate_exceptional_pvec_entries(mapping, = &pvec, indices);
          &nb= sp;   for (i =3D 0; i < pagevec_count(&pvec); = i++)
          &nb= sp;           trunc= ate_cleanup_page(pvec.pages[i]);
@@ -391,6 +392,20 @@ void = truncate_inode_pages_range(struct address_space *mapping,
          &nb= sp;           if = (xa_is_value(page))
          &nb= sp;            = ;       continue;

+ =             &n= bsp;         /*
+ =             &n= bsp;          * = Already truncated? We can find and get subpage
+ =             &n= bsp;          * of = file THP, of which the head page is truncated.
+ =             &n= bsp;          *
+ =             &n= bsp;          * In = addition, another race will be avoided, where
+ =             &n= bsp;          * = collapse_file rolls back when writer truncates the
+ =             &n= bsp;          * page = cache.
+ =             &n= bsp;          */
+ =             &n= bsp;         if = (page_mapping(page) !=3D mapping) {
+ =             &n= bsp;           &nbs= p;     /* Restart to make sure all gone */
+ =             &n= bsp;           &nbs= p;     index =3D start - 1;
+ =             &n= bsp;           &nbs= p;     continue;
+ =             &n= bsp;         }
+
          &nb= sp;           lock_= page(page);
          &nb= sp;           WARN_= ON(page_to_index(page) !=3D index);
          &nb= sp;           wait_= on_page_writeback(page);
=E2=80=94
1.8.3.1

Thanks,
Rongwei = Wang

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