linux-kernel - Re: [PATCH 12/29] xfs: enforce GFP_NOIO implicitly during nowait time update

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Message-ID: <ZOi4oV7Ho3y0106O@casper.infradead.org>
Date:   Fri, 25 Aug 2023 15:20:17 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Hao Xu <hao.xu@...ux.dev>
Cc:     io-uring@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Pavel Begunkov <asml.silence@...il.com>,
        Christian Brauner <brauner@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Stefan Roesch <shr@...com>, Clay Harris <bugs@...ycon.org>,
        Dave Chinner <david@...morbit.com>,
        "Darrick J . Wong" <djwong@...nel.org>,
        linux-fsdevel@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-cachefs@...hat.com,
        ecryptfs@...r.kernel.org, linux-nfs@...r.kernel.org,
        linux-unionfs@...r.kernel.org, bpf@...r.kernel.org,
        netdev@...r.kernel.org, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-btrfs@...r.kernel.org, codalist@...a.cs.cmu.edu,
        linux-f2fs-devel@...ts.sourceforge.net, cluster-devel@...hat.com,
        linux-mm@...ck.org, linux-nilfs@...r.kernel.org,
        devel@...ts.orangefs.org, linux-cifs@...r.kernel.org,
        samba-technical@...ts.samba.org, linux-mtd@...ts.infradead.org,
        Wanpeng Li <wanpengli@...cent.com>
Subject: Re: [PATCH 12/29] xfs: enforce GFP_NOIO implicitly during nowait
 time update

On Fri, Aug 25, 2023 at 09:54:14PM +0800, Hao Xu wrote:
> +++ b/fs/xfs/xfs_iops.c
> @@ -1037,6 +1037,8 @@ xfs_vn_update_time(
>  	int			log_flags = XFS_ILOG_TIMESTAMP;
>  	struct xfs_trans	*tp;
>  	int			error;
> +	int			old_pflags;
> +	bool			nowait = flags & S_NOWAIT;
>  
>  	trace_xfs_update_time(ip);
>  
> @@ -1049,13 +1051,18 @@ xfs_vn_update_time(
>  		log_flags |= XFS_ILOG_CORE;
>  	}
>  
> +	if (nowait)
> +		old_pflags = memalloc_noio_save();
> +
>  	error = xfs_trans_alloc(mp, &M_RES(mp)->tr_fsyncts, 0, 0, 0, &tp);

This is an abuse of the memalloc_noio_save() interface.  You shouldn't
be setting it around individual allocations; it's the part of the kernel
which decides "I can't afford to do I/O" that should be setting it.
In this case, it should probably be set by io_uring, way way way up at
the top.

But Jens didn't actually answer my question about that:

https://lore.kernel.org/all/ZMhZh2EYPMH1wIXX@casper.infradead.org/