linux-ext4 - Re: [RFCv3 1/4] ext4: fix ext4_dax_read/write inode locking sequence for IOCB

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Date:   Wed, 20 Nov 2019 13:51:16 +0100
From:   Jan Kara <jack@...e.cz>
To:     Ritesh Harjani <riteshh@...ux.ibm.com>
Cc:     jack@...e.cz, tytso@....edu, linux-ext4@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, mbobrowski@...browski.org
Subject: Re: [RFCv3 1/4] ext4: fix ext4_dax_read/write inode locking sequence
 for IOCB_NOWAIT

On Wed 20-11-19 10:30:21, Ritesh Harjani wrote:
> Apparently our current rwsem code doesn't like doing the trylock, then
> lock for real scheme.  So change our dax read/write methods to just do the
> trylock for the RWF_NOWAIT case.
> This seems to fix AIM7 regression in some scalable filesystems upto ~25%
> in some cases. Claimed in commit 942491c9e6d6 ("xfs: fix AIM7 regression")
> 
> Signed-off-by: Ritesh Harjani <riteshh@...ux.ibm.com>

Looks good to me. You can add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/ext4/file.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/ext4/file.c b/fs/ext4/file.c
> index 6a7293a5cda2..977ac58dc718 100644
> --- a/fs/ext4/file.c
> +++ b/fs/ext4/file.c
> @@ -88,9 +88,10 @@ static ssize_t ext4_dax_read_iter(struct kiocb *iocb, struct iov_iter *to)
>  	struct inode *inode = file_inode(iocb->ki_filp);
>  	ssize_t ret;
>  
> -	if (!inode_trylock_shared(inode)) {
> -		if (iocb->ki_flags & IOCB_NOWAIT)
> +	if (iocb->ki_flags & IOCB_NOWAIT) {
> +		if (!inode_trylock_shared(inode))
>  			return -EAGAIN;
> +	} else {
>  		inode_lock_shared(inode);
>  	}
>  	/*
> @@ -487,9 +488,10 @@ ext4_dax_write_iter(struct kiocb *iocb, struct iov_iter *from)
>  	bool extend = false;
>  	struct inode *inode = file_inode(iocb->ki_filp);
>  
> -	if (!inode_trylock(inode)) {
> -		if (iocb->ki_flags & IOCB_NOWAIT)
> +	if (iocb->ki_flags & IOCB_NOWAIT) {
> +		if (!inode_trylock(inode))
>  			return -EAGAIN;
> +	} else {
>  		inode_lock(inode);
>  	}
>  
> -- 
> 2.21.0
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR