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An issue can occur between write-streaming (storing dirty data in partial
non-uptodate pages) and a cachefiles object being culled to make space.
The problem occurs because the cache object is only marked in use while
there are files open using it. Once it has been released, it can be culled
and the cookie marked disabled.
At this point, a streaming write is permitted to occur (if the cache is
active, we require pages to be prefetched and cached), but the cache can
become active again before this gets flushed out - and then two effects can
occur:
(1) The cache may be asked to write out a region that's less than its DIO
block size (assumed by cachefiles to be PAGE_SIZE) - and this causes
one of two debugging statements to be emitted.
(2) netfs_how_to_modify() gets confused because it sees a page that isn't
allowed to be non-uptodate being uptodate and tries to prefetch it -
leading to a warning that PG_fscache is set twice.
Fix this by the following means:
(1) Add a netfs_inode flag to disallow write-streaming to an inode and set
it if we ever do local caching of that inode. It remains set for the
lifetime of that inode - even if the cookie becomes disabled.
(2) If the no-write-streaming flag is set, then make netfs_how_to_modify()
always want to prefetch instead.
(3) If netfs_how_to_modify() decides it wants to prefetch a folio, but
that folio has write-streamed data in it, then it requires the folio
be flushed first.
(4) Export a counter of the number of times we wanted to prefetch a
non-uptodate page, but found it had write-streamed data in it.
(5) Export a counter of the number of times we cancelled a write to the
cache because it didn't DIO align and remove the debug statements.
Reported-by: Marc Dionne <marc.dionne@auristor.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
cc: linux-erofs@lists.ozlabs.org
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
77 lines
2.6 KiB
C
77 lines
2.6 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/* Netfs support statistics
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*
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* Copyright (C) 2021 Red Hat, Inc. All Rights Reserved.
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* Written by David Howells (dhowells@redhat.com)
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*/
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#include <linux/export.h>
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#include <linux/seq_file.h>
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#include "internal.h"
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atomic_t netfs_n_rh_dio_read;
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atomic_t netfs_n_rh_dio_write;
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atomic_t netfs_n_rh_readahead;
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atomic_t netfs_n_rh_readpage;
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atomic_t netfs_n_rh_rreq;
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atomic_t netfs_n_rh_sreq;
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atomic_t netfs_n_rh_download;
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atomic_t netfs_n_rh_download_done;
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atomic_t netfs_n_rh_download_failed;
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atomic_t netfs_n_rh_download_instead;
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atomic_t netfs_n_rh_read;
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atomic_t netfs_n_rh_read_done;
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atomic_t netfs_n_rh_read_failed;
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atomic_t netfs_n_rh_zero;
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atomic_t netfs_n_rh_short_read;
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atomic_t netfs_n_rh_write;
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atomic_t netfs_n_rh_write_begin;
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atomic_t netfs_n_rh_write_done;
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atomic_t netfs_n_rh_write_failed;
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atomic_t netfs_n_rh_write_zskip;
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atomic_t netfs_n_wh_wstream_conflict;
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atomic_t netfs_n_wh_upload;
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atomic_t netfs_n_wh_upload_done;
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atomic_t netfs_n_wh_upload_failed;
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atomic_t netfs_n_wh_write;
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atomic_t netfs_n_wh_write_done;
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atomic_t netfs_n_wh_write_failed;
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int netfs_stats_show(struct seq_file *m, void *v)
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{
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seq_printf(m, "Netfs : DR=%u DW=%u RA=%u RP=%u WB=%u WBZ=%u\n",
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atomic_read(&netfs_n_rh_dio_read),
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atomic_read(&netfs_n_rh_dio_write),
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atomic_read(&netfs_n_rh_readahead),
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atomic_read(&netfs_n_rh_readpage),
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atomic_read(&netfs_n_rh_write_begin),
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atomic_read(&netfs_n_rh_write_zskip));
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seq_printf(m, "Netfs : ZR=%u sh=%u sk=%u\n",
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atomic_read(&netfs_n_rh_zero),
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atomic_read(&netfs_n_rh_short_read),
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atomic_read(&netfs_n_rh_write_zskip));
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seq_printf(m, "Netfs : DL=%u ds=%u df=%u di=%u\n",
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atomic_read(&netfs_n_rh_download),
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atomic_read(&netfs_n_rh_download_done),
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atomic_read(&netfs_n_rh_download_failed),
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atomic_read(&netfs_n_rh_download_instead));
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seq_printf(m, "Netfs : RD=%u rs=%u rf=%u\n",
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atomic_read(&netfs_n_rh_read),
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atomic_read(&netfs_n_rh_read_done),
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atomic_read(&netfs_n_rh_read_failed));
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seq_printf(m, "Netfs : UL=%u us=%u uf=%u\n",
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atomic_read(&netfs_n_wh_upload),
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atomic_read(&netfs_n_wh_upload_done),
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atomic_read(&netfs_n_wh_upload_failed));
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seq_printf(m, "Netfs : WR=%u ws=%u wf=%u\n",
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atomic_read(&netfs_n_wh_write),
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atomic_read(&netfs_n_wh_write_done),
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atomic_read(&netfs_n_wh_write_failed));
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seq_printf(m, "Netfs : rr=%u sr=%u wsc=%u\n",
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atomic_read(&netfs_n_rh_rreq),
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atomic_read(&netfs_n_rh_sreq),
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atomic_read(&netfs_n_wh_wstream_conflict));
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return fscache_stats_show(m);
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}
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EXPORT_SYMBOL(netfs_stats_show);
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