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Message-ID: <ZOu1xYS6LRmPgEiV@casper.infradead.org>
Date: Sun, 27 Aug 2023 21:44:53 +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,
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Wanpeng Li <wanpengli@...cent.com>
Subject: Re: [PATCH 02/11] xfs: add NOWAIT semantics for readdir
On Sun, Aug 27, 2023 at 09:28:26PM +0800, Hao Xu wrote:
> +++ b/fs/xfs/libxfs/xfs_da_btree.c
> @@ -2643,16 +2643,32 @@ xfs_da_read_buf(
> struct xfs_buf_map map, *mapp = ↦
> int nmap = 1;
> int error;
> + int buf_flags = 0;
>
> *bpp = NULL;
> error = xfs_dabuf_map(dp, bno, flags, whichfork, &mapp, &nmap);
> if (error || !nmap)
> goto out_free;
>
> + /*
> + * NOWAIT semantics mean we don't wait on the buffer lock nor do we
> + * issue IO for this buffer if it is not already in memory. Caller will
> + * retry. This will return -EAGAIN if the buffer is in memory and cannot
> + * be locked, and no buffer and no error if it isn't in memory. We
> + * translate both of those into a return state of -EAGAIN and *bpp =
> + * NULL.
> + */
I would not include this comment.
> + if (flags & XFS_DABUF_NOWAIT)
> + buf_flags |= XBF_TRYLOCK | XBF_INCORE;
> error = xfs_trans_read_buf_map(mp, tp, mp->m_ddev_targp, mapp, nmap, 0,
> &bp, ops);
what tsting did you do with this? Because you don't actually _use_
buf_flags anywhere in this patch (presumably they should be the
sixth argument to xfs_trans_read_buf_map() instead of 0). So I can only
conclude that either you didn't test, or your testing was inadequate.
> if (error)
> goto out_free;
> + if (!bp) {
> + ASSERT(flags & XFS_DABUF_NOWAIT);
I don't think this ASSERT is appropriate.
> @@ -391,10 +401,17 @@ xfs_dir2_leaf_getdents(
> bp = NULL;
> }
>
> - if (*lock_mode == 0)
> - *lock_mode = xfs_ilock_data_map_shared(dp);
> + if (*lock_mode == 0) {
> + *lock_mode =
> + xfs_ilock_data_map_shared_generic(dp,
> + ctx->flags & DIR_CONTEXT_F_NOWAIT);
> + if (!*lock_mode) {
> + error = -EAGAIN;
> + break;
> + }
> + }
'generic' doesn't seem like a great suffix to mean 'takes nowait flag'.
And this is far too far indented.
xfs_dir2_lock(dp, ctx, lock_mode);
with:
STATIC void xfs_dir2_lock(struct xfs_inode *dp, struct dir_context *ctx,
unsigned int lock_mode)
{
if (*lock_mode)
return;
if (ctx->flags & DIR_CONTEXT_F_NOWAIT)
return xfs_ilock_data_map_shared_nowait(dp);
return xfs_ilock_data_map_shared(dp);
}
... which I think you can use elsewhere in this patch (reformat it to
XFS coding style, of course). And then you don't need
xfs_ilock_data_map_shared_generic().
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