From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D14903AC36 for ; Tue, 20 Aug 2024 02:36:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724121418; cv=none; b=iXxuCmvmqygbOrMANv9HgxVh/ugrvQjhh58l5lULiON5U/Nr+ZxKPLbgO7NtxK1WBQjASM2pADvpVqPEEdaWSWvwZ1RhMs8dOmWrtHc8J1WGJoQefaKDZJcMSEgrUNN4op3a2z8VQKXCcMI7mT1duFbJqeuAsmR8XtWjnPJcuwY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724121418; c=relaxed/simple; bh=Sba57+zrm2Ini6LKTxC4ZAaVD76HRDZco4sXMSgoJYw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=gCPzfJwh1NnJ/V7mv3d+ccG1LyydqkM+g1o6Py6m+lfy3OEMX0GrBA1xA7KM83RSvOu62gpUX+af2Uootd2bN2w2Z3DoeKwq1PDqx4Te5CSl056z5c3aMK0n+TZP7PACjhFSVpnbCJ/Np3Qzk1XAYBWrfR2uUrl/BglcgaBMAu4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=V+fGdBRa; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="V+fGdBRa" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1724121413; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=QF1lmMHrhdZR6ZdXj97aq/HFFDSr1jt4s2hUL4XunTs=; b=V+fGdBRaMqC7CXzBL80YrIiy+3xKn7h3jaIBN8aZ1MqMhWWo/C8p+vYsWf0tX2BFbPJEyY yfLNJDW1oqxqsEkgm6V4xkUckFAb7/oZq1ROBSr4fLsSi10YqF8UdGcbop7qJo8+VWzoLy LEP22O+cCc/AjBToyy1W2PoIqwoOzgU= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-377-PwRuuHcNMgOdu1aLwcTb0Q-1; 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> Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 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