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Mon, 19 Aug 2024 22:36:48 -0400 X-MC-Unique: PwRuuHcNMgOdu1aLwcTb0Q-1 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 3F1F61955BEF; Tue, 20 Aug 2024 02:36:45 +0000 (UTC) Received: from fedora (unknown [10.72.116.107]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id B79E51954B3D; Tue, 20 Aug 2024 02:36:38 +0000 (UTC) Date: Tue, 20 Aug 2024 10:36:34 +0800 From: Ming Lei To: Jens Axboe Cc: Pavel Begunkov , io-uring@vger.kernel.org, Conrad Meyer , linux-block@vger.kernel.org, linux-mm@kvack.org, Jan Kara , Shin'ichiro Kawasaki Subject: Re: [RFC 5/5] block: implement io_uring discard cmd Message-ID: References: <6ecd7ab3386f63f1656dc766c1b5b038ff5353c2.1723601134.git.asml.silence@gmail.com> <4d016a30-d258-4d0e-b3bc-18bf0bd48e32@kernel.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 X-Stat-Signature: dgzdfs63bitp1qru6tg1tstq5iwwnja4 X-Rspamd-Queue-Id: 08940C0024 X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1724121414-476412 X-HE-Meta: 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 ehOmA+LL +D2xUA0xH8QPSQWfkw0RpzcorxVDEx7Jx4TBM5mBP1bNPsQKKTy3VwL5sl2dsxl+52kR4LQoEEaxjFFxawtKs4ctGNmeRN+1gJcC6Z1TA2guc/zPQCFB6GrxTbAkEVX8+d0Ni2mgXImmBpeEwtpfLEIFRgSaN+HRTcBtkPm18upsTAaaJNg74V0ElKnV6czCrCA6Dta8Q4VA4buQJFYis0gQRaQ9HSDWxFOzhZFbHrkw976m/lCoPca0XKRLmIc5z6vL0XVdjRbOTsASanNVHdBA5CrmD7VHM3RIBF2B9QSL8Mut8aiJgIoPS5QBy53bCAfOsC5Sjcp7rraMx7TL2dbHBULH9uWgFCNnnpI56MzBg+wmtAPeqLQ/xVWiztbZFMWN2uk89OZhzk3yvjQmECatcOe4TFhssoJE/OZv9+WSq1E33WpK+rPwlpA8pjUixg8OSrUta7pF0csfOcS1gHbAsf6ZmabKqo66okFGDHeXqL6k= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Aug 19, 2024 at 02:01:21PM -0600, Jens Axboe wrote: > On 8/15/24 7:45 PM, Ming Lei wrote: > > On Thu, Aug 15, 2024 at 07:24:16PM -0600, Jens Axboe wrote: > >> On 8/15/24 5:44 PM, Ming Lei wrote: > >>> On Thu, Aug 15, 2024 at 06:11:13PM +0100, Pavel Begunkov wrote: > >>>> On 8/15/24 15:33, Jens Axboe wrote: > >>>>> On 8/14/24 7:42 PM, Ming Lei wrote: > >>>>>> On Wed, Aug 14, 2024 at 6:46?PM Pavel Begunkov wrote: > >>>>>>> > >>>>>>> Add ->uring_cmd callback for block device files and use it to implement > >>>>>>> asynchronous discard. Normally, it first tries to execute the command > >>>>>>> from non-blocking context, which we limit to a single bio because > >>>>>>> otherwise one of sub-bios may need to wait for other bios, and we don't > >>>>>>> want to deal with partial IO. If non-blocking attempt fails, we'll retry > >>>>>>> it in a blocking context. > >>>>>>> > >>>>>>> Suggested-by: Conrad Meyer > >>>>>>> Signed-off-by: Pavel Begunkov > >>>>>>> --- > >>>>>>> block/blk.h | 1 + > >>>>>>> block/fops.c | 2 + > >>>>>>> block/ioctl.c | 94 +++++++++++++++++++++++++++++++++++++++++ > >>>>>>> include/uapi/linux/fs.h | 2 + > >>>>>>> 4 files changed, 99 insertions(+) > >>>>>>> > >>>>>>> diff --git a/block/blk.h b/block/blk.h > >>>>>>> index e180863f918b..5178c5ba6852 100644 > >>>>>>> --- a/block/blk.h > >>>>>>> +++ b/block/blk.h > >>>>>>> @@ -571,6 +571,7 @@ blk_mode_t file_to_blk_mode(struct file *file); > >>>>>>> int truncate_bdev_range(struct block_device *bdev, blk_mode_t mode, > >>>>>>> loff_t lstart, loff_t lend); > >>>>>>> long blkdev_ioctl(struct file *file, unsigned cmd, unsigned long arg); > >>>>>>> +int blkdev_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags); > >>>>>>> long compat_blkdev_ioctl(struct file *file, unsigned cmd, unsigned long arg); > >>>>>>> > >>>>>>> extern const struct address_space_operations def_blk_aops; > >>>>>>> diff --git a/block/fops.c b/block/fops.c > >>>>>>> index 9825c1713a49..8154b10b5abf 100644 > >>>>>>> --- a/block/fops.c > >>>>>>> +++ b/block/fops.c > >>>>>>> @@ -17,6 +17,7 @@ > >>>>>>> #include > >>>>>>> #include > >>>>>>> #include > >>>>>>> +#include > >>>>>>> #include "blk.h" > >>>>>>> > >>>>>>> static inline struct inode *bdev_file_inode(struct file *file) > >>>>>>> @@ -873,6 +874,7 @@ const struct file_operations def_blk_fops = { > >>>>>>> .splice_read = filemap_splice_read, > >>>>>>> .splice_write = iter_file_splice_write, > >>>>>>> .fallocate = blkdev_fallocate, > >>>>>>> + .uring_cmd = blkdev_uring_cmd, > >>>>>> > >>>>>> Just be curious, we have IORING_OP_FALLOCATE already for sending > >>>>>> discard to block device, why is .uring_cmd added for this purpose? > >>>> > >>>> Which is a good question, I haven't thought about it, but I tend to > >>>> agree with Jens. Because vfs_fallocate is created synchronous > >>>> IORING_OP_FALLOCATE is slow for anything but pretty large requests. > >>>> Probably can be patched up, which would involve changing the > >>>> fops->fallocate protot, but I'm not sure async there makes sense > >>>> outside of bdev (?), and cmd approach is simpler, can be made > >>>> somewhat more efficient (1 less layer in the way), and it's not > >>>> really something completely new since we have it in ioctl. > >>> > >>> Yeah, we have ioctl(DISCARD), which acquires filemap_invalidate_lock, > >>> same with blkdev_fallocate(). > >>> > >>> But this patch drops this exclusive lock, so it becomes async friendly, > >>> but may cause stale page cache. However, if the lock is required, it can't > >>> be efficient anymore and io-wq may be inevitable, :-) > >> > >> If you want to grab the lock, you can still opportunistically grab it. > >> For (by far) the common case, you'll get it, and you can still do it > >> inline. > > > > If the lock is grabbed in the whole cmd lifetime, it is basically one sync > > interface cause there is at most one async discard cmd in-flight for each > > device. > > Oh for sure, you could not do that anyway as you'd be holding a lock > across the syscall boundary, which isn't allowed. Indeed. > > > Meantime the handling has to move to io-wq for avoiding to block current > > context, the interface becomes same with IORING_OP_FALLOCATE? > > I think the current truncate is overkill, we should be able to get by > without. And no, I will not entertain an option that's "oh just punt it > to io-wq". BTW, the truncate is added by 351499a172c0 ("block: Invalidate cache on discard v2"), and block/009 serves as regression test for covering page cache coherency and discard. Here the issue is actually related with the exclusive lock of filemap_invalidate_lock(). IMO, it is reasonable to prevent page read during discard for not polluting page cache. block/009 may fail too without the lock. It is just that concurrent discards can't be allowed any more by down_write() of rw_semaphore, and block device is really capable of doing that. It can be thought as one regression of 7607c44c157d ("block: Hold invalidate_lock in BLKDISCARD ioctl"). Cc Jan Kara and Shin'ichiro Kawasaki. Thanks, Ming