user/sven/linux.git/include/linux/backing-dev-defs.h, branch v5.8.5

bdi: remove the name field in struct backing_dev_info

2020-05-09T22:15:13Z

The name is only printed for a not registered bdi in writeback. Use the device name there as is more useful anyway for the unlike case that the warning triggers. Signed-off-by: Christoph Hellwig Reviewed-by: Jan Kara Reviewed-by: Greg Kroah-Hartman Reviewed-by: Bart Van Assche Signed-off-by: Jens Axboe

bdi: add a ->dev_name field to struct backing_dev_info

2020-05-09T22:07:57Z

Cache a copy of the name for the life time of the backing_dev_info structure so that we can reference it even after unregistering. Fixes: 68f23b89067f ("memcg: fix a crash in wb_workfn when a device disappears") Reported-by: Yufen Yu Signed-off-by: Christoph Hellwig Reviewed-by: Jan Kara Reviewed-by: Bart Van Assche Signed-off-by: Jens Axboe

buffer: remove useless comment and WB_REASON_FREE_MORE_MEM, reason.

2020-04-18T03:38:11Z

free_more_memory func has been completely removed in commit bc48f001de12 ("buffer: eliminate the need to call free_more_memory() in __getblk_slow()") So comment and `WB_REASON_FREE_MORE_MEM` reason about free_more_memory are no longer needed. Fixes: bc48f001de12 ("buffer: eliminate the need to call free_more_memory() in __getblk_slow()") Reviewed-by: Jan Kara Signed-off-by: Zhiqiang Liu Signed-off-by: Jens Axboe

writeback, memcg: Implement foreign dirty flushing

2019-08-27T15:22:38Z

There's an inherent mismatch between memcg and writeback. The former trackes ownership per-page while the latter per-inode. This was a deliberate design decision because honoring per-page ownership in the writeback path is complicated, may lead to higher CPU and IO overheads and deemed unnecessary given that write-sharing an inode across different cgroups isn't a common use-case. Combined with inode majority-writer ownership switching, this works well enough in most cases but there are some pathological cases. For example, let's say there are two cgroups A and B which keep writing to different but confined parts of the same inode. B owns the inode and A's memory is limited far below B's. A's dirty ratio can rise enough to trigger balance_dirty_pages() sleeps but B's can be low enough to avoid triggering background writeback. A will be slowed down without a way to make writeback of the dirty pages happen. This patch implements foreign dirty recording and foreign mechanism so that when a memcg encounters a condition as above it can trigger flushes on bdi_writebacks which can clean its pages. Please see the comment on top of mem_cgroup_track_foreign_dirty_slowpath() for details. A reproducer follows. write-range.c:: #include #include #include #include #include static const char *usage = "write-range FILE START SIZE\n"; int main(int argc, char **argv) { int fd; unsigned long start, size, end, pos; char *endp; char buf[4096]; if (argc < 4) { fprintf(stderr, usage); return 1; } fd = open(argv[1], O_WRONLY); if (fd < 0) { perror("open"); return 1; } start = strtoul(argv[2], &endp, 0); if (*endp != '\0') { fprintf(stderr, usage); return 1; } size = strtoul(argv[3], &endp, 0); if (*endp != '\0') { fprintf(stderr, usage); return 1; } end = start + size; while (1) { for (pos = start; pos < end; ) { long bread, bwritten = 0; if (lseek(fd, pos, SEEK_SET) < 0) { perror("lseek"); return 1; } bread = read(0, buf, sizeof(buf) < end - pos ? sizeof(buf) : end - pos); if (bread < 0) { perror("read"); return 1; } if (bread == 0) return 0; while (bwritten < bread) { long this; this = write(fd, buf + bwritten, bread - bwritten); if (this < 0) { perror("write"); return 1; } bwritten += this; pos += bwritten; } } } } repro.sh:: #!/bin/bash set -e set -x sysctl -w vm.dirty_expire_centisecs=300000 sysctl -w vm.dirty_writeback_centisecs=300000 sysctl -w vm.dirtytime_expire_seconds=300000 echo 3 > /proc/sys/vm/drop_caches TEST=/sys/fs/cgroup/test A=$TEST/A B=$TEST/B mkdir -p $A $B echo "+memory +io" > $TEST/cgroup.subtree_control echo $((1<<30)) > $A/memory.high echo $((32<<30)) > $B/memory.high rm -f testfile touch testfile fallocate -l 4G testfile echo "Starting B" (echo $BASHPID > $B/cgroup.procs pv -q --rate-limit 70M < /dev/urandom | ./write-range testfile $((2<<30)) $((2<<30))) & echo "Waiting 10s to ensure B claims the testfile inode" sleep 5 sync sleep 5 sync echo "Starting A" (echo $BASHPID > $A/cgroup.procs pv < /dev/urandom | ./write-range testfile 0 $((2<<30))) v2: Added comments explaining why the specific intervals are being used. v3: Use 0 @nr when calling cgroup_writeback_by_id() to use best-effort flushing while avoding possible livelocks. v4: Use get_jiffies_64() and time_before/after64() instead of raw jiffies_64 and arthimetic comparisons as suggested by Jan. Reviewed-by: Jan Kara Signed-off-by: Tejun Heo Signed-off-by: Jens Axboe

bdi: Add bdi->id

2019-08-27T15:22:38Z

There currently is no way to universally identify and lookup a bdi without holding a reference and pointer to it. This patch adds an non-recycling bdi->id and implements bdi_get_by_id() which looks up bdis by their ids. This will be used by memcg foreign inode flushing. I left bdi_list alone for simplicity and because while rb_tree does support rcu assignment it doesn't seem to guarantee lossless walk when walk is racing aginst tree rebalance operations. Reviewed-by: Jan Kara Signed-off-by: Tejun Heo Signed-off-by: Jens Axboe

writeback: Generalize and expose wb_completion

2019-08-27T15:22:38Z

wb_completion is used to track writeback completions. We want to use it from memcg side for foreign inode flushes. This patch updates it to remember the target waitq instead of assuming bdi->wb_waitq and expose it outside of fs-writeback.c. Reviewed-by: Jan Kara Signed-off-by: Tejun Heo Signed-off-by: Jens Axboe

backing-dev: no need to check return value of debugfs_create functions

2019-06-03T13:49:07Z

When calling debugfs functions, there is no need to ever check the return value. The function can work or not, but the code logic should never do something different based on this. And as the return value does not matter at all, no need to save the dentry in struct backing_dev_info, so delete it. Cc: Andrew Morton Cc: Anders Roxell Cc: Arnd Bergmann Cc: Michal Hocko Cc: linux-mm@kvack.org Reviewed-by: Sebastian Andrzej Siewior Signed-off-by: Greg Kroah-Hartman

writeback: synchronize sync(2) against cgroup writeback membership switches

2019-01-22T21:39:38Z

sync_inodes_sb() can race against cgwb (cgroup writeback) membership switches and fail to writeback some inodes. For example, if an inode switches to another wb while sync_inodes_sb() is in progress, the new wb might not be visible to bdi_split_work_to_wbs() at all or the inode might jump from a wb which hasn't issued writebacks yet to one which already has. This patch adds backing_dev_info->wb_switch_rwsem to synchronize cgwb switch path against sync_inodes_sb() so that sync_inodes_sb() is guaranteed to see all the target wbs and inodes can't jump wbs to escape syncing. v2: Fixed misplaced rwsem init. Spotted by Jiufei. Signed-off-by: Tejun Heo Reported-by: Jiufei Xue Link: http://lkml.kernel.org/r/dc694ae2-f07f-61e1-7097-7c8411cee12d@gmail.com Acked-by: Jan Kara Signed-off-by: Jens Axboe

writeback: don't decrement wb->refcnt if !wb->bdi

2018-12-28T20:11:46Z

This happened while running in qemu-system-aarch64, the AMBA PL011 UART driver when enabling CONFIG_DEBUG_TEST_DRIVER_REMOVE. arch_initcall(pl011_init) came before subsys_initcall(default_bdi_init), devtmpfs' handle_remove() crashes because the reference count is a NULL pointer only because wb->bdi hasn't been initialized yet. Rework so that wb_put have an extra check if wb->bdi before decrement wb->refcnt and also add a WARN_ON_ONCE to get a warning if it happens again in other drivers. Link: http://lkml.kernel.org/r/20181030113545.30999-2-anders.roxell@linaro.org Fixes: 52ebea749aae ("writeback: make backing_dev_info host cgroup-specific bdi_writebacks") Signed-off-by: Arnd Bergmann Signed-off-by: Anders Roxell Co-developed-by: Arnd Bergmann Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

bdi: use refcount_t for reference counting instead atomic_t

2018-08-22T17:52:46Z

refcount_t type and corresponding API should be used instead of atomic_t when the variable is used as a reference counter. This permits avoiding accidental refcounter overflows that might lead to use-after-free situations. Link: http://lkml.kernel.org/r/20180703200141.28415-4-bigeasy@linutronix.de Signed-off-by: Sebastian Andrzej Siewior Reviewed-by: Andrew Morton Acked-by: Peter Zijlstra (Intel) Suggested-by: Peter Zijlstra Cc: Jens Axboe Cc: Ingo Molnar Cc: Thomas Gleixner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds