The patch titled Subject: aio: document, clarify aio_read_events() and shadow_tail has been added to the -mm tree. Its filename is aio-document-clarify-aio_read_events-and-shadow_tail.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Kent Overstreet <koverstreet@xxxxxxxxxx> Subject: aio: document, clarify aio_read_events() and shadow_tail Signed-off-by: Kent Overstreet <koverstreet@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- fs/aio.c | 34 ++++++++++++++++++++++++++++------ 1 file changed, 28 insertions(+), 6 deletions(-) diff -puN fs/aio.c~aio-document-clarify-aio_read_events-and-shadow_tail fs/aio.c --- a/fs/aio.c~aio-document-clarify-aio_read_events-and-shadow_tail +++ a/fs/aio.c @@ -103,6 +103,19 @@ struct kioctx { struct { struct mutex ring_lock; wait_queue_head_t wait; + + /* + * Copy of the real tail, that aio_complete uses - to reduce + * cacheline bouncing. The real tail will tend to be much more + * contended - since typically events are delivered one at a + * time, and then aio_read_events() slurps them up a bunch at a + * time - so it's helpful if aio_read_events() isn't also + * contending for the tail. So, aio_complete() updates + * shadow_tail whenever it updates tail. + * + * Also needed because tail is used as a hacky lock and isn't + * always the real tail. + */ unsigned shadow_tail; } ____cacheline_aligned_in_smp; @@ -846,10 +859,7 @@ static long aio_read_events_ring(struct long ret = 0; int copy_ret; - if (!mutex_trylock(&ctx->ring_lock)) { - __set_current_state(TASK_RUNNING); - mutex_lock(&ctx->ring_lock); - } + mutex_lock(&ctx->ring_lock); ring = kmap_atomic(ctx->ring_pages[0]); head = ring->head; @@ -860,8 +870,6 @@ static long aio_read_events_ring(struct if (head == ctx->shadow_tail) goto out; - __set_current_state(TASK_RUNNING); - while (ret < nr) { long avail = (head < ctx->shadow_tail ? ctx->shadow_tail : ctx->nr) - head; @@ -940,6 +948,20 @@ static long read_events(struct kioctx *c until = timespec_to_ktime(ts); } + /* + * Note that aio_read_events() is being called as the conditional - i.e. + * we're calling it after prepare_to_wait() has set task state to + * TASK_INTERRUPTIBLE. + * + * But aio_read_events() can block, and if it blocks it's going to flip + * the task state back to TASK_RUNNING. + * + * This should be ok, provided it doesn't flip the state back to + * TASK_RUNNING and return 0 too much - that causes us to spin. That + * will only happen if the mutex_lock() call blocks, and we then find + * the ringbuffer empty. So in practice we should be ok, but it's + * something to be aware of when touching this code. + */ wait_event_interruptible_hrtimeout(ctx->wait, aio_read_events(ctx, min_nr, nr, event, &ret), until); _ Patches currently in -mm which might be from koverstreet@xxxxxxxxxx are jiffies-conversions-use-compile-time-constants-when-possible.patch mm-remove-old-aio-use_mm-comment.patch aio-remove-dead-code-from-aioh.patch gadget-remove-only-user-of-aio-retry.patch aio-remove-retry-based-aio.patch char-add-aio_readwrite-to-dev-nullzero.patch aio-kill-return-value-of-aio_complete.patch aio-kiocb_cancel.patch aio-kiocb_cancel-fix.patch aio-move-private-stuff-out-of-aioh.patch aio-dprintk-pr_debug.patch aio-do-fget-after-aio_get_req.patch aio-make-aio_put_req-lockless.patch aio-refcounting-cleanup.patch wait-add-wait_event_hrtimeout.patch wait-add-wait_event_hrtimeout-fix.patch aio-make-aio_read_evt-more-efficient-convert-to-hrtimers.patch aio-use-flush_dcache_page.patch aio-use-cancellation-list-lazily.patch aio-change-reqs_active-to-include-unreaped-completions.patch aio-kill-batch-allocation.patch aio-kill-struct-aio_ring_info.patch aio-give-shared-kioctx-fields-their-own-cachelines.patch aio-give-shared-kioctx-fields-their-own-cachelines-fix.patch aio-reqs_active-reqs_available.patch aio-percpu-reqs_available.patch generic-dynamic-per-cpu-refcounting.patch generic-dynamic-per-cpu-refcounting-fix.patch generic-dynamic-per-cpu-refcounting-fix-fix.patch aio-percpu-ioctx-refcount.patch aio-use-xchg-instead-of-completion_lock.patch aio-dont-include-aioh-in-schedh.patch aio-dont-include-aioh-in-schedh-fix.patch aio-dont-include-aioh-in-schedh-fix-fix.patch aio-dont-include-aioh-in-schedh-fix-3.patch aio-kill-ki_key.patch aio-kill-ki_retry.patch aio-kill-ki_retry-fix.patch block-aio-batch-completion-for-bios-kiocbs.patch block-aio-batch-completion-for-bios-kiocbs-fix.patch block-aio-batch-completion-for-bios-kiocbs-fix-fix.patch block-aio-batch-completion-for-bios-kiocbs-fix-fix-fix.patch block-aio-batch-completion-for-bios-kiocbs-fix-fix-fix-fix.patch virtio-blk-convert-to-batch-completion.patch mtip32xx-convert-to-batch-completion.patch aio-smoosh-struct-kiocb.patch aio-smoosh-struct-kiocb-fix.patch aio-fix-aio_read_events_ring-types.patch aio-document-clarify-aio_read_events-and-shadow_tail.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html