在 2022/2/15 上午1:43, Stefan Roesch 写道:
This patch series adds support for async buffered writes. Currently io-uring only supports buffered writes in the slow path, by processing them in the io workers. With this patch series it is now possible to support buffered writes in the fast path. To be able to use the fast path the required pages must be in the page cache or they can be loaded with noio. Otherwise they still get punted to the slow path. If a buffered write request requires more than one page, it is possible that only part of the request can use the fast path, the resst will be completed by the io workers. Support for async buffered writes: Patch 1: fs: Add flags parameter to __block_write_begin_int Add a flag parameter to the function __block_write_begin_int to allow specifying a nowait parameter.Patch 2: mm: Introduce do_generic_perform_writeIntroduce a new do_generic_perform_write function. The function is split off from the existing generic_perform_write() function. It allows to specify an additional flag parameter. This parameter is used to specify the nowait flag.Patch 3: mm: add noio support in filemap_get_pagesThis allows to allocate pages with noio, if a page for async buffered writes is not yet loaded in the page cache.Patch 4: mm: Add support for async buffered writesFor async buffered writes allocate pages without blocking on the allocation. Patch 5: fs: split off __alloc_page_buffers function Split off __alloc_page_buffers() function with new gfp_t parameter. Patch 6: fs: split off __create_empty_buffers function Split off __create_empty_buffers() function with new gfp_t parameter. Patch 7: fs: Add aop_flags parameter to create_page_buffers() Add aop_flags to create_page_buffers() function. Use atomic allocation for async buffered writes. Patch 8: fs: add support for async buffered writes Return -EAGAIN instead of -ENOMEM for async buffered writes. This will cause the write request to be processed by an io worker. Patch 9: io_uring: add support for async buffered writes This enables the async buffered writes for block devices in io_uring. Buffered writes are enabled for blocks that are already in the page cache or can be acquired with noio. Patch 10: io_uring: Add tracepoint for short writes Support for write throttling of async buffered writes: Patch 11: sched: add new fields to task_struct Add two new fields to the task_struct. These fields store the deadline after which writes are no longer throttled. Patch 12: mm: support write throttling for async buffered writes This changes the balance_dirty_pages function to take an additonal parameter. When nowait is specified the write throttling code no longer waits synchronously for the deadline to expire. Instead it sets the fields in task_struct. Once the deadline expires the fields are reset.Patch 13: io_uring: support write throttling for async buffered writesAdds support to io_uring for write throttling. When the writes are throttled, the write requests are added to the pending io list. Once the write throttling deadline expires, the writes are submitted.Enable async buffered write supportPatch 14: fs: add flag to support async buffered writes This sets the flags that enables async buffered writes for block devices. Testing: This patch has been tested with xfstests and fio. Peformance results: For fio the following results have been obtained with a queue depth of 1 and 4k block size (runtime 600 secs): sequential writes: without patch with patch throughput: 329 Mib/s 1032Mib/s iops: 82k 264k slat (nsec) 2332 3340 clat (nsec) 9017 60CPU util%: 37% 78%random writes: without patch with patch throughput: 307 Mib/s 909Mib/s iops: 76k 227k slat (nsec) 2419 3780 clat (nsec) 9934 59 CPU util%: 57% 88% For an io depth of 1, the new patch improves throughput by close to 3 times and also the latency is considerably reduced. To achieve the same or better performance with the exisiting code an io depth of 4 is required. Especially for mixed workloads this is a considerable improvement. Stefan Roesch (14): fs: Add flags parameter to __block_write_begin_int mm: Introduce do_generic_perform_write mm: add noio support in filemap_get_pages mm: Add support for async buffered writes fs: split off __alloc_page_buffers function fs: split off __create_empty_buffers function fs: Add aop_flags parameter to create_page_buffers() fs: add support for async buffered writes io_uring: add support for async buffered writes io_uring: Add tracepoint for short writes sched: add new fields to task_struct mm: support write throttling for async buffered writes io_uring: support write throttling for async buffered writes block: enable async buffered writes for block devices. block/fops.c | 5 +- fs/buffer.c | 103 ++++++++++++++++--------- fs/internal.h | 3 +- fs/io_uring.c | 130 +++++++++++++++++++++++++++++--- fs/iomap/buffered-io.c | 4 +- fs/read_write.c | 3 +- include/linux/fs.h | 4 + include/linux/sched.h | 3 + include/linux/writeback.h | 1 + include/trace/events/io_uring.h | 25 ++++++ kernel/fork.c | 1 + mm/filemap.c | 34 +++++++-- mm/folio-compat.c | 4 + mm/page-writeback.c | 54 +++++++++---- 14 files changed, 298 insertions(+), 76 deletions(-) base-commit: f1baf68e1383f6ed93eb9cff2866d46562607a43
It's a little bit different between buffered read and buffered write, there may be block points in detail filesystems due to journal operations for the latter.
