Message ID | 20220619151143.1054746-2-willy@infradead.org (mailing list archive) |
---|---|
State | New, archived |
Headers | show |
Series | Fixes for 5.19b | expand |
On Sun, Jun 19, 2022 at 04:11:41PM +0100, Matthew Wilcox (Oracle) wrote: > +static inline bool pos_same_folio(loff_t pos1, loff_t pos2, struct folio *folio) > > +{ > + unsigned int shift = folio_shift(folio); > + > + return (pos1 >> shift == pos2 >> shift); > +} The calling convention with the folio as the last argument seems a bit odd to me. But then again so does passing just one folio for checking if something is in the same folio. But as I can't come up with something better I'll just deposit these mumblings here insted of actually complaining.
Greeting, FYI, we noticed a -8.9% regression of phoronix-test-suite.fio.SequentialRead.LinuxAIO.Yes.No.4KB.DefaultTestDirectory.mb_s due to commit: commit: 91fd26c76b86231276b6d7ac71d02d6fde78e297 ("[PATCH 1/3] filemap: Correct the conditions for marking a folio as accessed") url: https://github.com/intel-lab-lkp/linux/commits/Matthew-Wilcox-Oracle/Fixes-for-5-19b/20220619-231336 base: https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git 4b35035bcf80ddb47c0112c4fbd84a63a2836a18 patch link: https://lore.kernel.org/linux-mm/20220619151143.1054746-2-willy@infradead.org in testcase: phoronix-test-suite on test machine: 96 threads 2 sockets Intel(R) Xeon(R) Gold 6252 CPU @ 2.10GHz with 512G memory with following parameters: test: fio-1.14.1 option_a: Sequential Read option_b: Linux AIO option_c: Yes option_d: No option_e: 4KB option_f: Default Test Directory cpufreq_governor: performance ucode: 0x500320a test-description: The Phoronix Test Suite is the most comprehensive testing and benchmarking platform available that provides an extensible framework for which new tests can be easily added. test-url: http://www.phoronix-test-suite.com/ If you fix the issue, kindly add following tag Reported-by: kernel test robot <oliver.sang@intel.com> Details are as below: --------------------------------------------------------------------------------------------------> To reproduce: git clone https://github.com/intel/lkp-tests.git cd lkp-tests sudo bin/lkp install job.yaml # job file is attached in this email bin/lkp split-job --compatible job.yaml # generate the yaml file for lkp run sudo bin/lkp run generated-yaml-file # if come across any failure that blocks the test, # please remove ~/.lkp and /lkp dir to run from a clean state. ========================================================================================= compiler/cpufreq_governor/kconfig/option_a/option_b/option_c/option_d/option_e/option_f/rootfs/tbox_group/test/testcase/ucode: gcc-11/performance/x86_64-rhel-8.3/Sequential Read/Linux AIO/Yes/No/4KB/Default Test Directory/debian-x86_64-phoronix/lkp-csl-2sp7/fio-1.14.1/phoronix-test-suite/0x500320a commit: 4b35035bcf ("Merge tag 'nfs-for-5.19-2' of git://git.linux-nfs.org/projects/anna/linux-nfs") 91fd26c76b ("filemap: Correct the conditions for marking a folio as accessed") 4b35035bcf80ddb4 91fd26c76b86231276b6d7ac71d ---------------- --------------------------- %stddev %change %stddev \ | \ 477611 -8.9% 435055 phoronix-test-suite.fio.SequentialRead.LinuxAIO.Yes.No.4KB.DefaultTestDirectory.iops 1865 -8.9% 1699 phoronix-test-suite.fio.SequentialRead.LinuxAIO.Yes.No.4KB.DefaultTestDirectory.mb_s 2.871e+08 -8.8% 2.619e+08 phoronix-test-suite.time.file_system_inputs 925561 +45.0% 1342367 ± 4% numa-meminfo.node0.Active 89584 ± 15% +466.8% 507739 ± 11% numa-meminfo.node0.Active(file) 22395 ± 15% +464.5% 126419 ± 11% numa-vmstat.node0.nr_active_file 22395 ± 15% +464.5% 126422 ± 11% numa-vmstat.node0.nr_zone_active_file 1168858 -8.9% 1064851 vmstat.io.bi 20386 -7.7% 18809 vmstat.system.cs 950958 +43.6% 1365179 ± 3% meminfo.Active 112156 +369.8% 526961 ± 7% meminfo.Active(file) 2764971 -14.5% 2364011 meminfo.Inactive 1502049 -26.2% 1108866 meminfo.Inactive(file) 31273678 -7.0% 29071736 perf-stat.i.cache-misses 20797 -7.8% 19169 perf-stat.i.context-switches 6002418 -8.5% 5491342 perf-stat.i.node-loads 6357381 -7.6% 5874070 perf-stat.i.node-stores 239.46 ± 9% +14.4% 273.86 ± 5% perf-stat.overall.cycles-between-cache-misses 30990966 -7.1% 28805139 perf-stat.ps.cache-misses 20608 -7.8% 18993 perf-stat.ps.context-switches 5947870 -8.5% 5440625 perf-stat.ps.node-loads 6299557 -7.6% 5819731 perf-stat.ps.node-stores 28038 +370.1% 131814 ± 7% proc-vmstat.nr_active_file 98818 -1.6% 97280 proc-vmstat.nr_anon_pages 375391 -26.2% 277223 proc-vmstat.nr_inactive_file 28038 +370.1% 131814 ± 7% proc-vmstat.nr_zone_active_file 375391 -26.2% 277223 proc-vmstat.nr_zone_inactive_file 511.83 ± 14% +79.3% 917.83 ± 63% proc-vmstat.numa_hint_faults_local 40090769 -7.8% 36977817 proc-vmstat.numa_hit 39810116 -7.7% 36751505 proc-vmstat.numa_local 316086 +10350.9% 33034013 proc-vmstat.pgactivate 39795174 -7.9% 36645119 proc-vmstat.pgalloc_normal 39417989 -8.0% 36280723 proc-vmstat.pgfree 1.436e+08 -8.8% 1.31e+08 proc-vmstat.pgpgin 18.38 ± 10% -2.5 15.86 ± 2% perf-profile.calltrace.cycles-pp.ret_from_fork 18.38 ± 10% -2.5 15.86 ± 2% perf-profile.calltrace.cycles-pp.kthread.ret_from_fork 17.11 ± 10% -2.5 14.62 ± 2% perf-profile.calltrace.cycles-pp.worker_thread.kthread.ret_from_fork 15.09 ± 10% -2.4 12.67 ± 2% perf-profile.calltrace.cycles-pp.loop_process_work.process_one_work.worker_thread.kthread.ret_from_fork 15.28 ± 10% -2.4 12.88 ± 2% perf-profile.calltrace.cycles-pp.process_one_work.worker_thread.kthread.ret_from_fork 14.03 ± 9% -2.3 11.71 ± 3% perf-profile.calltrace.cycles-pp.do_iter_read.loop_process_work.process_one_work.worker_thread.kthread 13.60 ± 9% -2.2 11.36 ± 2% perf-profile.calltrace.cycles-pp.do_iter_readv_writev.do_iter_read.loop_process_work.process_one_work.worker_thread 13.51 ± 9% -2.2 11.28 ± 2% perf-profile.calltrace.cycles-pp.shmem_file_read_iter.do_iter_readv_writev.do_iter_read.loop_process_work.process_one_work 11.84 ± 9% -1.9 9.90 ± 3% perf-profile.calltrace.cycles-pp.copy_page_to_iter.shmem_file_read_iter.do_iter_readv_writev.do_iter_read.loop_process_work 11.76 ± 9% -1.9 9.83 ± 3% perf-profile.calltrace.cycles-pp._copy_to_iter.copy_page_to_iter.shmem_file_read_iter.do_iter_readv_writev.do_iter_read 0.00 +0.6 0.62 ± 4% perf-profile.calltrace.cycles-pp.__folio_activate.pagevec_lru_move_fn.folio_mark_accessed.filemap_read.aio_read 0.00 +0.7 0.71 ± 6% perf-profile.calltrace.cycles-pp.workingset_activation.folio_mark_accessed.filemap_read.aio_read.io_submit_one 0.00 +1.1 1.14 ± 5% perf-profile.calltrace.cycles-pp.pagevec_lru_move_fn.folio_mark_accessed.filemap_read.aio_read.io_submit_one 11.35 ± 8% +1.5 12.80 ± 2% perf-profile.calltrace.cycles-pp.filemap_read.aio_read.io_submit_one.__x64_sys_io_submit.do_syscall_64 0.26 ±100% +2.3 2.54 ± 6% perf-profile.calltrace.cycles-pp.folio_mark_accessed.filemap_read.aio_read.io_submit_one.__x64_sys_io_submit 51.18 ± 2% +2.3 53.50 perf-profile.calltrace.cycles-pp.cpuidle_enter_state.cpuidle_enter.cpuidle_idle_call.do_idle.cpu_startup_entry 56.89 ± 2% +2.4 59.30 perf-profile.calltrace.cycles-pp.secondary_startup_64_no_verify 56.38 ± 2% +2.4 58.79 perf-profile.calltrace.cycles-pp.do_idle.cpu_startup_entry.start_secondary.secondary_startup_64_no_verify 56.40 ± 2% +2.4 58.82 perf-profile.calltrace.cycles-pp.cpu_startup_entry.start_secondary.secondary_startup_64_no_verify 56.40 ± 2% +2.4 58.82 perf-profile.calltrace.cycles-pp.start_secondary.secondary_startup_64_no_verify 55.10 ± 3% +2.5 57.56 perf-profile.calltrace.cycles-pp.cpuidle_idle_call.do_idle.cpu_startup_entry.start_secondary.secondary_startup_64_no_verify 18.39 ± 10% -2.5 15.86 ± 2% perf-profile.children.cycles-pp.ret_from_fork 18.38 ± 10% -2.5 15.86 ± 2% perf-profile.children.cycles-pp.kthread 17.11 ± 10% -2.5 14.62 ± 2% perf-profile.children.cycles-pp.worker_thread 15.11 ± 10% -2.4 12.69 ± 2% perf-profile.children.cycles-pp.loop_process_work 15.28 ± 10% -2.4 12.88 ± 2% perf-profile.children.cycles-pp.process_one_work 14.04 ± 9% -2.3 11.72 ± 2% perf-profile.children.cycles-pp.do_iter_read 13.61 ± 9% -2.2 11.36 ± 2% perf-profile.children.cycles-pp.do_iter_readv_writev 13.52 ± 9% -2.2 11.28 ± 2% perf-profile.children.cycles-pp.shmem_file_read_iter 15.62 ± 5% -2.2 13.40 ± 2% perf-profile.children.cycles-pp.copy_page_to_iter 11.78 ± 9% -1.9 9.84 ± 3% perf-profile.children.cycles-pp._copy_to_iter 1.07 ± 10% -0.2 0.92 ± 4% perf-profile.children.cycles-pp.shmem_getpage_gfp 0.53 ± 5% -0.1 0.39 ± 11% perf-profile.children.cycles-pp.security_file_permission 0.46 ± 5% -0.1 0.32 ± 13% perf-profile.children.cycles-pp.apparmor_file_permission 0.32 ± 6% -0.1 0.25 ± 9% perf-profile.children.cycles-pp.touch_atime 0.26 ± 6% -0.1 0.20 ± 11% perf-profile.children.cycles-pp.atime_needs_update 0.50 -0.1 0.45 ± 5% perf-profile.children.cycles-pp.free_pcppages_bulk 0.38 ± 6% -0.0 0.33 ± 2% perf-profile.children.cycles-pp.ksys_read 0.42 ± 5% -0.0 0.38 ± 5% perf-profile.children.cycles-pp.read_tsc 0.37 ± 6% -0.0 0.33 perf-profile.children.cycles-pp.vfs_read 0.24 ± 9% -0.0 0.21 ± 2% perf-profile.children.cycles-pp.seq_read_iter 0.13 ± 6% -0.0 0.10 ± 14% perf-profile.children.cycles-pp.current_time 0.12 ± 5% -0.0 0.10 ± 8% perf-profile.children.cycles-pp.__libc_read 0.02 ±141% +0.1 0.08 ± 22% perf-profile.children.cycles-pp.mem_cgroup_update_lru_size 0.02 ±142% +0.1 0.08 ± 9% perf-profile.children.cycles-pp.folio_lruvec_lock_irqsave 0.00 +0.1 0.07 ± 18% perf-profile.children.cycles-pp.__count_memcg_events 0.17 ± 12% +0.1 0.26 ± 7% perf-profile.children.cycles-pp.__mod_node_page_state 0.25 ± 13% +0.1 0.37 ± 8% perf-profile.children.cycles-pp.__mod_lruvec_state 2.61 ± 5% +0.3 2.86 ± 4% perf-profile.children.cycles-pp.tick_sched_timer 2.04 ± 6% +0.3 2.32 ± 7% perf-profile.children.cycles-pp.update_process_times 0.00 +0.5 0.46 ± 11% perf-profile.children.cycles-pp.workingset_age_nonresident 0.00 +0.6 0.64 ± 4% perf-profile.children.cycles-pp.__folio_activate 0.00 +0.7 0.72 ± 7% perf-profile.children.cycles-pp.workingset_activation 0.00 +1.1 1.14 ± 5% perf-profile.children.cycles-pp.pagevec_lru_move_fn 0.51 ± 9% +2.1 2.59 ± 6% perf-profile.children.cycles-pp.folio_mark_accessed 56.89 ± 2% +2.4 59.29 perf-profile.children.cycles-pp.do_idle 56.89 ± 2% +2.4 59.30 perf-profile.children.cycles-pp.secondary_startup_64_no_verify 56.89 ± 2% +2.4 59.30 perf-profile.children.cycles-pp.cpu_startup_entry 56.40 ± 2% +2.4 58.82 perf-profile.children.cycles-pp.start_secondary 55.60 ± 2% +2.5 58.06 perf-profile.children.cycles-pp.cpuidle_idle_call 11.69 ± 9% -1.9 9.78 ± 3% perf-profile.self.cycles-pp._copy_to_iter 0.37 ± 6% -0.1 0.24 ± 15% perf-profile.self.cycles-pp.apparmor_file_permission 0.13 ± 12% -0.0 0.10 ± 14% perf-profile.self.cycles-pp.atime_needs_update 0.08 ± 17% +0.0 0.11 ± 6% perf-profile.self.cycles-pp.__mod_lruvec_state 0.18 ± 12% +0.1 0.26 ± 12% perf-profile.self.cycles-pp.__mod_memcg_lruvec_state 0.16 ± 14% +0.1 0.25 ± 8% perf-profile.self.cycles-pp.__mod_node_page_state 0.49 ± 9% +0.2 0.71 ± 9% perf-profile.self.cycles-pp.folio_mark_accessed 0.00 +0.2 0.25 ± 5% perf-profile.self.cycles-pp.workingset_activation 0.00 +0.3 0.30 ± 9% perf-profile.self.cycles-pp.pagevec_lru_move_fn 0.00 +0.3 0.34 ± 9% perf-profile.self.cycles-pp.__folio_activate 0.00 +0.5 0.46 ± 11% perf-profile.self.cycles-pp.workingset_age_nonresident Disclaimer: Results have been estimated based on internal Intel analysis and are provided for informational purposes only. Any difference in system hardware or software design or configuration may affect actual performance.
Hi Willy, linux-btrfs@vger, Matthew Wilcox (Oracle) wrote on Sun, Jun 19, 2022 at 04:11:41PM +0100: > We had an off-by-one error which meant that we never marked the first page > in a read as accessed. This was visible as a slowdown when re-reading > a file as pages were being evicted from cache too soon. In reviewing > this code, we noticed a second bug where a multi-page folio would be > marked as accessed multiple times when doing reads that were less than > the size of the folio. when debugging an unrelated issue (short reads on btrfs with io_uring and O_DIRECT[1]), I noticed that my horrible big file copy speeds fell down from ~2GB/s (there's compression and lots of zeroes) to ~100MB/s the second time I was copying it with cp. I've taken a moment to bisect this and came down to this patch. [1] https://lore.kernel.org/all/YrrFGO4A1jS0GI0G@atmark-techno.com/T/#u Dropping caches (echo 3 > /proc/sys/vm/drop_caches) restore the speed, so there appears to be some bad effect to having the file in cache for fiemap? To be fair that file is pretty horrible: --- # compsize bigfile Processed 1 file, 194955 regular extents (199583 refs), 0 inline. Type Perc Disk Usage Uncompressed Referenced TOTAL 15% 3.7G 23G 23G none 100% 477M 477M 514M zstd 14% 3.2G 23G 23G --- Here's what perf has to say about it on top of this patch when running `cp bigfile /dev/null` the first time: 98.97% 0.00% cp [kernel.kallsyms] [k] entry_SYSCALL_64_after_hwframe entry_SYSCALL_64_after_hwframe do_syscall_64 - 93.40% ksys_read - 93.36% vfs_read - 93.25% new_sync_read - 93.20% filemap_read - 83.38% filemap_get_pages - 82.76% page_cache_ra_unbounded + 59.72% folio_alloc + 13.43% read_pages + 8.75% filemap_add_folio 0.64% xa_load 0.52% filemap_get_read_batch + 8.75% copy_page_to_iter - 4.73% __x64_sys_ioctl - 4.72% do_vfs_ioctl - btrfs_fiemap - 4.70% extent_fiemap + 3.95% btrfs_check_shared + 0.70% get_extent_skip_holes and second time: 99.90% 0.00% cp [kernel.kallsyms] [k] entry_SYSCALL_64_after_hwfram entry_SYSCALL_64_after_hwframe do_syscall_64 - 94.62% __x64_sys_ioctl do_vfs_ioctl btrfs_fiemap - extent_fiemap - 50.01% get_extent_skip_holes - 50.00% btrfs_get_extent_fiemap - 49.97% count_range_bits rb_next + 28.72% lock_extent_bits + 15.55% __clear_extent_bit - 5.21% ksys_read + 5.21% vfs_read (if this isn't readable, 95% of the time is spent on fiemap the second time around) I've also been observing RCU stalls on my laptop with the same workload (cp to /dev/null), but unfortunately I could not reproduce in qemu so I could not take traces to confirm they are caused by the same commit but given the workload I'd say that is it? I can rebuild a kernel for my laptop and confirm if you think it should be something else. I didn't look at the patch itself (yet) so have no suggestion at this point - it's plausible the patch fixed something and just exposed slow code that had been there all along so it might be better to look at the btrfs side first, I don't know. If you don't manage to reproduce I'll be happy to test anything thrown at me at the very least. Thanks,
On Thu, Jun 30, 2022 at 04:29:05PM +0900, Dominique MARTINET wrote: > Hi Willy, linux-btrfs@vger, > > Matthew Wilcox (Oracle) wrote on Sun, Jun 19, 2022 at 04:11:41PM +0100: > > We had an off-by-one error which meant that we never marked the first page > > in a read as accessed. This was visible as a slowdown when re-reading > > a file as pages were being evicted from cache too soon. In reviewing > > this code, we noticed a second bug where a multi-page folio would be > > marked as accessed multiple times when doing reads that were less than > > the size of the folio. > > when debugging an unrelated issue (short reads on btrfs with io_uring > and O_DIRECT[1]), I noticed that my horrible big file copy speeds fell > down from ~2GB/s (there's compression and lots of zeroes) to ~100MB/s > the second time I was copying it with cp. > > I've taken a moment to bisect this and came down to this patch. I think you may have forgotten to include the commit-id that was the results of your bisect.... ? - Ted
Theodore Ts'o wrote on Thu, Jun 30, 2022 at 10:37:58AM -0400: > On Thu, Jun 30, 2022 at 04:29:05PM +0900, Dominique MARTINET wrote: > > Hi Willy, linux-btrfs@vger, > > > > Matthew Wilcox (Oracle) wrote on Sun, Jun 19, 2022 at 04:11:41PM +0100: > > > We had an off-by-one error which meant that we never marked the first page > > > in a read as accessed. This was visible as a slowdown when re-reading > > > a file as pages were being evicted from cache too soon. In reviewing > > > this code, we noticed a second bug where a multi-page folio would be > > > marked as accessed multiple times when doing reads that were less than > > > the size of the folio. > > > > when debugging an unrelated issue (short reads on btrfs with io_uring > > and O_DIRECT[1]), I noticed that my horrible big file copy speeds fell > > down from ~2GB/s (there's compression and lots of zeroes) to ~100MB/s > > the second time I was copying it with cp. > > > > I've taken a moment to bisect this and came down to this patch. > > I think you may have forgotten to include the commit-id that was the > results of your bisect.... ? Sorry, this is the patch I replied to and it was recent enough that I assumed it'd still be in mailboxes, but you're right it's better with a commit id. This is was merged as 5ccc944dce3d ("filemap: Correct the conditions for marking a folio as accessed") Thanks,
在 2022/06/30 15:29, Dominique MARTINET 写道: > Hi Willy, linux-btrfs@vger, > > Matthew Wilcox (Oracle) wrote on Sun, Jun 19, 2022 at 04:11:41PM +0100: >> We had an off-by-one error which meant that we never marked the first page >> in a read as accessed. This was visible as a slowdown when re-reading >> a file as pages were being evicted from cache too soon. In reviewing >> this code, we noticed a second bug where a multi-page folio would be >> marked as accessed multiple times when doing reads that were less than >> the size of the folio. > > when debugging an unrelated issue (short reads on btrfs with io_uring > and O_DIRECT[1]), I noticed that my horrible big file copy speeds fell > down from ~2GB/s (there's compression and lots of zeroes) to ~100MB/s > the second time I was copying it with cp. > Hi, With this patch ctive_page() will be called the second time that page is mark accessed, which has some extra overhead, however, 2GB/s -> 100MB/s is insane, I'm not sure how this is possible, but it seems like it has something to do with this change.(Noted that it's problematic that page will not mark accessed before this patch). BTW, during my test, the speed of buffer read in ext4 only fell down a little. Thanks, Kuai > I've taken a moment to bisect this and came down to this patch. > > [1] https://lore.kernel.org/all/YrrFGO4A1jS0GI0G@atmark-techno.com/T/#u > > > > Dropping caches (echo 3 > /proc/sys/vm/drop_caches) restore the speed, > so there appears to be some bad effect to having the file in cache for > fiemap? > To be fair that file is pretty horrible: > --- > # compsize bigfile > Processed 1 file, 194955 regular extents (199583 refs), 0 inline. > Type Perc Disk Usage Uncompressed Referenced > TOTAL 15% 3.7G 23G 23G > none 100% 477M 477M 514M > zstd 14% 3.2G 23G 23G > --- > > Here's what perf has to say about it on top of this patch when running > `cp bigfile /dev/null` the first time: > > 98.97% 0.00% cp [kernel.kallsyms] [k] > entry_SYSCALL_64_after_hwframe > entry_SYSCALL_64_after_hwframe > do_syscall_64 > - 93.40% ksys_read > - 93.36% vfs_read > - 93.25% new_sync_read > - 93.20% filemap_read > - 83.38% filemap_get_pages > - 82.76% page_cache_ra_unbounded > + 59.72% folio_alloc > + 13.43% read_pages > + 8.75% filemap_add_folio > 0.64% xa_load > 0.52% filemap_get_read_batch > + 8.75% copy_page_to_iter > - 4.73% __x64_sys_ioctl > - 4.72% do_vfs_ioctl > - btrfs_fiemap > - 4.70% extent_fiemap > + 3.95% btrfs_check_shared > + 0.70% get_extent_skip_holes > > and second time: > 99.90% 0.00% cp [kernel.kallsyms] [k] > entry_SYSCALL_64_after_hwfram > entry_SYSCALL_64_after_hwframe > do_syscall_64 > - 94.62% __x64_sys_ioctl > do_vfs_ioctl > btrfs_fiemap > - extent_fiemap > - 50.01% get_extent_skip_holes > - 50.00% btrfs_get_extent_fiemap > - 49.97% count_range_bits > rb_next > + 28.72% lock_extent_bits > + 15.55% __clear_extent_bit > - 5.21% ksys_read > + 5.21% vfs_read > > (if this isn't readable, 95% of the time is spent on fiemap the second > time around) > > > > > I've also been observing RCU stalls on my laptop with the same workload > (cp to /dev/null), but unfortunately I could not reproduce in qemu so I > could not take traces to confirm they are caused by the same commit but > given the workload I'd say that is it? > I can rebuild a kernel for my laptop and confirm if you think it should > be something else. > > > I didn't look at the patch itself (yet) so have no suggestion at this > point - it's plausible the patch fixed something and just exposed slow > code that had been there all along so it might be better to look at the > btrfs side first, I don't know. > If you don't manage to reproduce I'll be happy to test anything thrown > at me at the very least. > > > Thanks, >
(added btrfs maintainers in direct cc) Yu Kuai wrote on Fri, Jul 01, 2022 at 09:55:31AM +0800: > With this patch ctive_page() will be called the second time that page is > mark accessed, which has some extra overhead, however, 2GB/s -> 100MB/s > is insane, I'm not sure how this is possible, but it seems like it has > something to do with this change.(Noted that it's problematic that page > will not mark accessed before this patch). I honestly don't understand why folio being marked as accessed affects how fiemap is processed... My guess would be that this indeed "just fixes" that pages didn't get marked as accessed -> were dropped from cache -> it kept the inode io_tree small -> fiemap was fast ; and it really just a problem that the fiemap algorithm doesn't scale, but I haven't really checked if I'm right here. So I don't think we should focus so much on the regression part as to figure out what's actually different the second time around and make that faster. checking with 'perf script' btrfs_get_extent_fiemap() spends most of its time on this: delalloc_len = count_range_bits(&inode->io_tree, &delalloc_start, end, len, EXTENT_DELALLOC, 1); I have no idea what delalloc is supposed to be, but I can guess there is just way too many nodes in the io_tree: why is that and why wasn't there so many the first time around? I would assumed that as the file gets read it is put into cache, so the end of the first read should slow down as well but it didn't, so I'm sure I misunderstood something and I'm wasting everyone's time. Feel free to ignore me and find the issue instead :) > BTW, during my test, the speed of buffer read in ext4 only fell down a > little. For "normal" files that don't have ~200k extents full of holes and compression changes and whatever else this has gone through, I can confirm the slowdown is not as bad -- almost unnoticeable when few extents. but I still have my laptop cashing when I'm copying this file twice (well, I -could- just turn off panic_on_stall...) so it can go from a little to infinity... Thanks, (Leaving rest of the message for anyone catching up now; if there's anything you'd like me to do feel free to ask.) > > I've taken a moment to bisect this and came down to this patch. > > (5ccc944dce3d ("filemap: Correct the conditions for marking a folio > > as accessed")) > > > > [1] https://lore.kernel.org/all/YrrFGO4A1jS0GI0G@atmark-techno.com/T/#u > > > > > > > > Dropping caches (echo 3 > /proc/sys/vm/drop_caches) restore the speed, > > so there appears to be some bad effect to having the file in cache for > > fiemap? > > To be fair that file is pretty horrible: > > --- > > # compsize bigfile > > Processed 1 file, 194955 regular extents (199583 refs), 0 inline. > > Type Perc Disk Usage Uncompressed Referenced > > TOTAL 15% 3.7G 23G 23G > > none 100% 477M 477M 514M > > zstd 14% 3.2G 23G 23G > > --- > > > > Here's what perf has to say about it on top of this patch when running > > `cp bigfile /dev/null` the first time: > > > > 98.97% 0.00% cp [kernel.kallsyms] [k] > > entry_SYSCALL_64_after_hwframe > > entry_SYSCALL_64_after_hwframe > > do_syscall_64 > > - 93.40% ksys_read > > - 93.36% vfs_read > > - 93.25% new_sync_read > > - 93.20% filemap_read > > - 83.38% filemap_get_pages > > - 82.76% page_cache_ra_unbounded > > + 59.72% folio_alloc > > + 13.43% read_pages > > + 8.75% filemap_add_folio > > 0.64% xa_load > > 0.52% filemap_get_read_batch > > + 8.75% copy_page_to_iter > > - 4.73% __x64_sys_ioctl > > - 4.72% do_vfs_ioctl > > - btrfs_fiemap > > - 4.70% extent_fiemap > > + 3.95% btrfs_check_shared > > + 0.70% get_extent_skip_holes > > > > and second time: > > 99.90% 0.00% cp [kernel.kallsyms] [k] > > entry_SYSCALL_64_after_hwfram > > entry_SYSCALL_64_after_hwframe > > do_syscall_64 > > - 94.62% __x64_sys_ioctl > > do_vfs_ioctl > > btrfs_fiemap > > - extent_fiemap > > - 50.01% get_extent_skip_holes > > - 50.00% btrfs_get_extent_fiemap > > - 49.97% count_range_bits > > rb_next > > + 28.72% lock_extent_bits > > + 15.55% __clear_extent_bit > > - 5.21% ksys_read > > + 5.21% vfs_read > > > > (if this isn't readable, 95% of the time is spent on fiemap the second > > time around) > > > > > > > > > > I've also been observing RCU stalls on my laptop with the same workload > > (cp to /dev/null), but unfortunately I could not reproduce in qemu so I > > could not take traces to confirm they are caused by the same commit but > > given the workload I'd say that is it? > > I can rebuild a kernel for my laptop and confirm if you think it should > > be something else. > > > > > > I didn't look at the patch itself (yet) so have no suggestion at this > > point - it's plausible the patch fixed something and just exposed slow > > code that had been there all along so it might be better to look at the > > btrfs side first, I don't know. > > If you don't manage to reproduce I'll be happy to test anything thrown > > at me at the very least.
diff --git a/mm/filemap.c b/mm/filemap.c index ac3775c1ce4c..577068868449 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2629,6 +2629,13 @@ static int filemap_get_pages(struct kiocb *iocb, struct iov_iter *iter, return err; } +static inline bool pos_same_folio(loff_t pos1, loff_t pos2, struct folio *folio) +{ + unsigned int shift = folio_shift(folio); + + return (pos1 >> shift == pos2 >> shift); +} + /** * filemap_read - Read data from the page cache. * @iocb: The iocb to read. @@ -2700,11 +2707,11 @@ ssize_t filemap_read(struct kiocb *iocb, struct iov_iter *iter, writably_mapped = mapping_writably_mapped(mapping); /* - * When a sequential read accesses a page several times, only + * When a read accesses the same folio several times, only * mark it as accessed the first time. */ - if (iocb->ki_pos >> PAGE_SHIFT != - ra->prev_pos >> PAGE_SHIFT) + if (!pos_same_folio(iocb->ki_pos, ra->prev_pos - 1, + fbatch.folios[0])) folio_mark_accessed(fbatch.folios[0]); for (i = 0; i < folio_batch_count(&fbatch); i++) {