block: enable RWF_DONTCACHE for block devices#912
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vfsci-bot[bot] wants to merge 3 commits intovfs.base.cifrom
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block: enable RWF_DONTCACHE for block devices#912vfsci-bot[bot] wants to merge 3 commits intovfs.base.cifrom
vfsci-bot[bot] wants to merge 3 commits intovfs.base.cifrom
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Some bio completion handlers need to run in task context but bio_endio() can be called from IRQ context (e.g. buffer_head writeback). Add a BIO_COMPLETE_IN_TASK flag that bio submitters can set to request task-context completion of their bi_end_io callback. When bio_endio() sees this flag and is running in non-task context, it queues the bio to a per-cpu list and schedules a work item to call bi_end_io() from task context. A CPU hotplug dead callback drains any remaining bios from the departing CPU's batch. This will be used to enable RWF_DONTCACHE for block devices, and could be used for other subsystems like fscrypt that need task-context bio completion. Suggested-by: Matthew Wilcox <willy@infradead.org> Signed-off-by: Tal Zussman <tz2294@columbia.edu>
Set BIO_COMPLETE_IN_TASK on iomap writeback bios when IOMAP_IOEND_DONTCACHE is set. This ensures that bi_end_io runs in task context, where folio_end_dropbehind() can safely invalidate folios. With the bio layer now handling task-context deferral generically, XFS no longer needs to route DONTCACHE ioends through its completion workqueue for page cache invalidation. Remove the DONTCACHE check from xfs_ioend_needs_wq_completion(). Signed-off-by: Tal Zussman <tz2294@columbia.edu>
Block device buffered reads and writes already pass through filemap_read() and iomap_file_buffered_write() respectively, both of which handle IOCB_DONTCACHE. Enable RWF_DONTCACHE for block device files by setting FOP_DONTCACHE in def_blk_fops. For CONFIG_BUFFER_HEAD=y paths, add block_write_begin_iocb() which threads the kiocb through so that buffer_head-based I/O can use DONTCACHE behavior. The existing block_write_begin() is preserved as a wrapper that passes a NULL iocb. Set BIO_COMPLETE_IN_TASK in submit_bh_wbc() when the folio has dropbehind so that buffer_head writeback completions get deferred to task context. CONFIG_BUFFER_HEAD=n paths are handled by the previously added iomap BIO_COMPLETE_IN_TASK support. This support is useful for databases that operate on raw block devices, among other userspace applications. Signed-off-by: Tal Zussman <tz2294@columbia.edu>
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Series: https://patchwork.kernel.org/project/linux-fsdevel/list/?series=1072511
Submitter: Tal Zussman
Version: 4
Patches: 3/3
Message-ID:
<20260325-blk-dontcache-v4-0-c4b56db43f64@columbia.edu>Base: vfs.base.ci
Lore: https://lore.kernel.org/linux-fsdevel/20260325-blk-dontcache-v4-0-c4b56db43f64@columbia.edu
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