We've been using NFS with FS-Cache to act as a caching proxy (re-export). When under load we've encountered an issue where all the nfsd processes seem to get stuck in I/O wait. The proxy is running an older version of the nfs-fscache-nfsfs branch taken from 17th Nov 2022, https://github.com/DaveWysochanskiRH/kernel/commit/52acbd4584d1b83c844371e48de1a1e39d255a6d. The proxy mounts the source NFS server using NFS v3 with FS-Cache enabled. The clients mount the proxy using NFS v4.2 to avoid issues with file handle sizes. dmesg suggests that most of the CPU tasks are blocked by nfsd on folio_wait_bit_common INFO: task nfsd:180059 blocked for more than 120 seconds. Not tainted 6.1.0-rc5+ #1 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. task:nfsd state:D stack:0 pid:180059 ppid:2 flags:0x00004000 Call Trace: <TASK> __schedule+0x31e/0x14a0 ? _raw_spin_unlock_irqrestore+0x27/0x50 schedule+0x6b/0x110 io_schedule+0x46/0x80 folio_wait_bit_common+0x124/0x340 ? xas_find+0x7c/0x1e0 ? xas_find_marked+0x1f7/0x370 ? filemap_invalidate_unlock_two+0x50/0x50 folio_wait_private_2+0x2c/0x50 nfs_release_folio+0x5e/0xb0 [nfs] filemap_release_folio+0x66/0x80 invalidate_inode_pages2_range+0x240/0x400 invalidate_inode_pages2+0x17/0x20 nfs_clear_invalid_mapping+0x1d8/0x2d0 [nfs] nfs_revalidate_mapping+0x55/0x70 [nfs] nfs_file_read+0x4c/0xc0 [nfs] generic_file_splice_read+0x8f/0x160 do_splice_to+0x7d/0xc0 splice_direct_to_actor+0xad/0x210 ? fsid_source+0x60/0x60 [nfsd] ? nfsd_file_do_acquire+0xacf/0xbd0 [nfsd] nfsd_splice_read+0x7c/0x120 [nfsd] nfsd_read+0x147/0x1b0 [nfsd] nfsd3_proc_read+0x1b5/0x2d0 [nfsd] ? svcxdr_decode_nfs_fh3+0x4e/0x130 [nfsd] nfsd_dispatch+0x173/0x2b0 [nfsd] svc_process_common+0x3c8/0x620 [sunrpc] ? nfsd_svc+0x3e0/0x3e0 [nfsd] ? nfsd_shutdown_threads+0xb0/0xb0 [nfsd] svc_process+0xb2/0x100 [sunrpc] nfsd+0xda/0x190 [nfsd] kthread+0xfa/0x130 ? kthread_complete_and_exit+0x20/0x20 ret_from_fork+0x1f/0x30 </TASK> Checking /proc/PID/stack for all the nfsd processes had the following counts: * 72 - nfsd_file_do_acquire+0x20b/0xbd0 * 36 - folio_wait_bit_common+0x124/0x340 * 10 - fscache_begin_operation.part.0+0x288/0x2b0 [fscache] * 8 - __fscache_use_cookie+0x2e5/0x320 [fscache] * 2 - ext4_llseek+0x91/0x110 dmesg also contains a lot of errors about timeouts waiting for the cookie state to change: FS-Cache: fscache_begin_operation: cookie state change wait timed out: cookie->state=1 state=1 FS-Cache: O-cookie c=0026b915 [fl=602c na=1 nA=2 s=L] FS-Cache: O-cookie V=00000001 [Infs,3.0,2,,8335540a,6465ebb4,,,d0,100000,100000,249f0,249f0,249f0,249f0,1] FS-Cache: O-key=[32] 'b4eb6564010000005509a81a02000000ffffffff000000000400fd0301000000' FS-Cache: fscache_begin_operation: cookie state change wait timed out: cookie->state=1 state=1 FS-Cache: O-cookie c=0024fd88 [fl=602c na=1 nA=2 s=L] FS-Cache: O-cookie V=00000001 [Infs,3.0,2,,8335540a,6465ebb4,,,d0,100000,100000,249f0,249f0,249f0,249f0,1] FS-Cache: O-key=[32] 'b4eb6564010000007df7aa1702000000ffffffff000000000400fd0301000000' FS-Cache: fscache_begin_operation: cookie state change wait timed out: cookie->state=1 state=1 FS-Cache: O-cookie c=0026d61a [fl=4024 na=1 nA=2 s=L] FS-Cache: O-cookie V=00000001 [Infs,3.0,2,,8335540a,6465ebb4,,,d0,100000,100000,249f0,249f0,249f0,249f0,1] FS-Cache: O-key=[32] 'b4eb656401000000b79947ce01000000ffffffff000000000400fd0301000000' The clients were shutdown but the proxy instance kept for further diagnosis. The nfsd sockets remained stuck in CLOSE_WAIT, and the nfsd processes remained stuck on various tasks for at least 4 days. It seems at some point over the weekend the issue resolved itself and now all the nfsd threads are idle. I'm going to try to see if I can reproduce this on the latest versions of the patches with the lockdep enabled. Though currently we've only seen this issue while the system is under a heavy production workload (rendering) after several days. On Thu, 23 Mar 2023 at 17:50, David Wysochanski <dwysocha@xxxxxxxxxx> wrote: > > On Mon, Feb 20, 2023 at 8:43 AM Dave Wysochanski <dwysocha@xxxxxxxxxx> wrote: > > > > Trond, this v11 patchset addresses your latest feedback on patch #2, > > and I did a little bit of cleanup to patch 3 (see Changes notes below). > > I'm not sure of further changes to patch #3 without a more in-depth > > review with specifics, if you feel the current approach is unacceptable [1]. > > > > Trond and/or Anna, > > Have you had a chance to review this patchset and do you have further > concerns? > > Note that patch #3 will require a small fixup to apply after v6.3-rc1 > due to this commit: > 8bb7cd842c44 nfs: use bvec_set_page to initialize bvecs > > There is also still the small open issue of netfs counting read_bytes > in its unlock page path, but I view that as a netfs issue. I'll followup > with David Howells on that. > > > > Ben and Daire, if you could test this set and provide you feedback > > and a Tested-By: that would be appreciated. This set addresses > > the existing NFS + fscache performance concerns seen by a few > > users [5], which is due to utilization use of the deprecated > > single-page function, fscache_fallback_read_page(). However, > > until "known issue #1" below is also resolved, even with these > > patches, performance of NFS+fscache will still be a problem > > in some scenarios. > > > > This patchset converts NFS with fscache buffered read IO paths to > > use the netfs API with a non-invasive approach. The existing NFS pgio > > layer does not need extensive changes, and is the best way so far I've > > found to address Trond's previous concerns about modifying the IO > > path [2] as well as only enabling netfs when fscache is configured > > and enabled [3]. I have not attempted performance comparisions to > > address Chuck Lever's concern [4] because we are not converting the > > non-fscache enabled NFS IO paths to netfs. > > > > The patchset is based on Trond's latest 'testing' branch which includes > > his folio patchset, and is based on 6.2-rc5. It has been pushed to > > github at: > > https://github.com/DaveWysochanskiRH/kernel/commits/nfs-fscache-netfs > > https://github.com/DaveWysochanskiRH/kernel/commit/6424e4f139652b7552eff26eb5da1f2282d35616 > > > > Changes since v10 [6] > > ===================== > > PATCH6: Dropped > > PATCH1: Rename nfs_pageio_add_page to nfs_read_add_folio > > PATCH2: Use anonymous union to add struct netfs_inode to nfs_inode (Trond) [7] > > PATCH3: Change nfs_netfs_readpage_release() to nfs_netfs_folio_unlock() > > > > Testing > > ======= > > I did a full round of testing on this because it was rebased on top of > > Trond's testing branch which included his folio series. > > All of my unit tests pass except the one with the known issue #1 below. > > Multiple runs of xfstests generic tests (applicable to NFS) were run with > > with various servers, both with and without fscache enabled, and > > compared to baseline (Trond's testing branch). No new failures were > > observed with these patches, and in some xfstest instances, this > > patchset improves the results (some tests that were failing now pass). > > - hammerspace(pNFS flexfiles): NFS4.1, NFS4.2 > > - NetApp(pNFS filelayout): NFS4.1, NFS4.0, NFS3 > > - RHEL9: NFS4.2, NFS4.1, NFS4.0, NFS3 > > > > Known issues > > ============ > > 1. Unit test setting rsize < readahead does not properly read from > > fscache but re-reads data from the NFS server > > * This will be fixed with another dhowells patch [8]: > > "[PATCH v6 2/2] mm, netfs, fscache: Stop read optimisation when folio removed from pagecache" > > * Daire Byrne verified the patch fixes his issue as well > > > > 2. "Cache volume key already in use" after xfstest runs involving multiple mounts > > * Simple reproducer requires just two mounts as follows: > > mount -overs=4.1,fsc,nosharecache -o context=system_u:object_r:root_t:s0 nfs-server:/exp1 /mnt1 > > mount -overs=4.1,fsc,nosharecache -o context=system_u:object_r:root_t:s0 nfs-server:/exp2 /mnt2 > > * This should be fixed with dhowells patch [9]: > > "[PATCH v5] vfs, security: Fix automount superblock LSM init problem, preventing NFS sb sharing" > > > > > > References > > ========== > > [1] https://lore.kernel.org/linux-nfs/0676ecb2bb708e6fc29dbbe6b44551d6a0d021dc.camel@xxxxxxxxxx/ > > [2] https://lore.kernel.org/linux-nfs/9cfd5bc3cfc6abc2d3316b0387222e708d67f595.camel@xxxxxxxxxxxxxxx/ > > [3] https://lore.kernel.org/linux-nfs/da9200f1bded9b8b078a7aef227fd6b92eb028fb.camel@xxxxxxxxxxxxxxx/ > > [4] https://lore.kernel.org/linux-nfs/0A640C47-5F51-47E8-864D-E0E980F8B310@xxxxxxxxxx/ > > [5] https://lore.kernel.org/linux-nfs/CA+QRt4tPqH87NVkoETLjxieGjZ_f7XxRj+xS3NVxcJ+b8AAKQg@xxxxxxxxxxxxxx/ > > [6] https://lore.kernel.org/linux-nfs/20221103161637.1725471-1-dwysocha@xxxxxxxxxx/ > > [7] https://lore.kernel.org/linux-nfs/4d60636f62df4f5c200666ed2d1a5f2414c18e1f.camel@xxxxxxxxxx/ > > [8] https://lore.kernel.org/linux-nfs/20230216150701.3654894-1-dhowells@xxxxxxxxxx/T/#mf3807fa68fb6d495b87dde0d76b5237833a0cc81 > > [9] https://lore.kernel.org/linux-kernel/217595.1662033775@xxxxxxxxxxxxxxxxxxxxxx/ > > > > Dave Wysochanski (5): > > NFS: Rename readpage_async_filler to nfs_read_add_folio > > NFS: Configure support for netfs when NFS fscache is configured > > NFS: Convert buffered read paths to use netfs when fscache is enabled > > NFS: Remove all NFSIOS_FSCACHE counters due to conversion to netfs API > > NFS: Remove fscache specific trace points and NFS_INO_FSCACHE bit > > > > fs/nfs/Kconfig | 1 + > > fs/nfs/fscache.c | 242 ++++++++++++++++++++++--------------- > > fs/nfs/fscache.h | 131 ++++++++++++++------ > > fs/nfs/inode.c | 2 + > > fs/nfs/internal.h | 9 ++ > > fs/nfs/iostat.h | 17 --- > > fs/nfs/nfstrace.h | 91 -------------- > > fs/nfs/pagelist.c | 4 + > > fs/nfs/read.c | 105 ++++++++-------- > > fs/nfs/super.c | 11 -- > > include/linux/nfs_fs.h | 25 ++-- > > include/linux/nfs_iostat.h | 12 -- > > include/linux/nfs_page.h | 3 + > > include/linux/nfs_xdr.h | 3 + > > 14 files changed, 317 insertions(+), 339 deletions(-) > > > > -- > > 2.31.1 > > > > -- > > Linux-cachefs mailing list > > Linux-cachefs@xxxxxxxxxx > > https://listman.redhat.com/mailman/listinfo/linux-cachefs > > > > -- > Linux-cachefs mailing list > Linux-cachefs@xxxxxxxxxx > https://listman.redhat.com/mailman/listinfo/linux-cachefs
