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    SubjectRe: [RFC PATCH 1/2] mm, vmscan: account the number of isolated pages per zone
    On Fri, Feb 03, 2017 at 03:50:09PM +0100, Michal Hocko wrote:
    > [Let's CC more xfs people]
    >
    > On Fri 03-02-17 19:57:39, Tetsuo Handa wrote:
    > [...]
    > > (1) I got an assertion failure.
    >
    > I suspect this is a result of
    > http://lkml.kernel.org/r/20170201092706.9966-2-mhocko@kernel.org
    > I have no idea what the assert means though.
    >
    > >
    > > [ 969.626518] Killed process 6262 (oom-write) total-vm:2166856kB, anon-rss:1128732kB, file-rss:4kB, shmem-rss:0kB
    > > [ 969.958307] oom_reaper: reaped process 6262 (oom-write), now anon-rss:0kB, file-rss:0kB, shmem-rss:0kB
    > > [ 972.114644] XFS: Assertion failed: oldlen > newlen, file: fs/xfs/libxfs/xfs_bmap.c, line: 2867

    Indirect block reservation underrun on delayed allocation extent merge.
    These are extra blocks are used for the inode bmap btree when a delalloc
    extent is converted to physical blocks. We're in a case where we expect
    to only ever free excess blocks due to a merge of extents with
    independent reservations, but a situation occurs where we actually need
    blocks and hence the assert fails. This can occur if an extent is merged
    with one that has a reservation less than the expected worst case
    reservation for its size (due to previous extent splits due to hole
    punches, for example). Therefore, I think the core expectation that
    xfs_bmap_add_extent_hole_delay() will always have enough blocks
    pre-reserved is invalid.

    Can you describe the workload that reproduces this? FWIW, I think the
    way xfs_bmap_add_extent_hole_delay() currently works is likely broken
    and have a couple patches to fix up indlen reservation that I haven't
    posted yet. The diff that deals with this particular bit is appended.
    Care to give that a try?

    Brian

    > > [ 972.125085] ------------[ cut here ]------------
    > > [ 972.129261] WARNING: CPU: 0 PID: 6280 at fs/xfs/xfs_message.c:105 asswarn+0x33/0x40 [xfs]
    > > [ 972.136146] Modules linked in: nf_conntrack_netbios_ns nf_conntrack_broadcast ip6t_rpfilter ipt_REJECT nf_reject_ipv4 ip6t_REJECT nf_reject_ipv6 xt_conntrack coretemp crct10dif_pclmul ppdev crc32_pclmul ghash_clmulni_intel ip_set nfnetlink ebtable_nat aesni_intel crypto_simd cryptd ebtable_broute glue_helper vmw_balloon bridge stp llc ip6table_nat nf_conntrack_ipv6 nf_defrag_ipv6 pcspkr nf_nat_ipv6 ip6table_mangle ip6table_raw iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack iptable_mangle iptable_raw ebtable_filter ebtables ip6table_filter ip6_tables iptable_filter sg parport_pc parport shpchp i2c_piix4 vmw_vsock_vmci_transport vsock vmw_vmci ip_tables xfs libcrc32c sr_mod cdrom ata_generic sd_mod pata_acpi crc32c_intel serio_raw vmwgfx drm_kms_helper syscopyarea sysfillrect
    > > [ 972.163630] sysimgblt fb_sys_fops ttm drm ata_piix ahci libahci mptspi scsi_transport_spi mptscsih e1000 libata i2c_core mptbase
    > > [ 972.172535] CPU: 0 PID: 6280 Comm: write Not tainted 4.10.0-rc6-next-20170202 #498
    > > [ 972.175126] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 07/02/2015
    > > [ 972.178381] Call Trace:
    ...

    ---8<---

    diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
    index bfc00de..d2e48ed 100644
    --- a/fs/xfs/libxfs/xfs_bmap.c
    +++ b/fs/xfs/libxfs/xfs_bmap.c
    @@ -2809,7 +2809,8 @@ xfs_bmap_add_extent_hole_delay(
    oldlen = startblockval(left.br_startblock) +
    startblockval(new->br_startblock) +
    startblockval(right.br_startblock);
    - newlen = xfs_bmap_worst_indlen(ip, temp);
    + newlen = XFS_FILBLKS_MIN(xfs_bmap_worst_indlen(ip, temp),
    + oldlen);
    xfs_bmbt_set_startblock(xfs_iext_get_ext(ifp, *idx),
    nullstartblock((int)newlen));
    trace_xfs_bmap_post_update(ip, *idx, state, _THIS_IP_);
    @@ -2830,7 +2831,8 @@ xfs_bmap_add_extent_hole_delay(
    xfs_bmbt_set_blockcount(xfs_iext_get_ext(ifp, *idx), temp);
    oldlen = startblockval(left.br_startblock) +
    startblockval(new->br_startblock);
    - newlen = xfs_bmap_worst_indlen(ip, temp);
    + newlen = XFS_FILBLKS_MIN(xfs_bmap_worst_indlen(ip, temp),
    + oldlen);
    xfs_bmbt_set_startblock(xfs_iext_get_ext(ifp, *idx),
    nullstartblock((int)newlen));
    trace_xfs_bmap_post_update(ip, *idx, state, _THIS_IP_);
    @@ -2846,7 +2848,8 @@ xfs_bmap_add_extent_hole_delay(
    temp = new->br_blockcount + right.br_blockcount;
    oldlen = startblockval(new->br_startblock) +
    startblockval(right.br_startblock);
    - newlen = xfs_bmap_worst_indlen(ip, temp);
    + newlen = XFS_FILBLKS_MIN(xfs_bmap_worst_indlen(ip, temp),
    + oldlen);
    xfs_bmbt_set_allf(xfs_iext_get_ext(ifp, *idx),
    new->br_startoff,
    nullstartblock((int)newlen), temp, right.br_state);
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