Re: [PATCH 20/24] xfs: xfs_iflush() is no longer necessary

Darrick J. Wong
2020-05-22T23:54:53Z

On Fri, May 22, 2020 at 01:50:25PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> Now we have a cached buffer on inode log items, we don't need
> to do buffer lookups when flushing inodes anymore - all we need
> to do is lock the buffer and we are ready to go.
>
> This largely gets rid of the need for xfs_iflush(), which is
> essentially just a mechanism to look up the buffer and flush the
> inode to it. Instead, we can just call xfs_iflush_cluster() with a
> few modifications to ensure it also flushes the inode we already
> hold locked.
>
> This allows the AIL inode item pushing to be almost entirely
> non-blocking in XFS - we won't block unless memory allocation
> for the cluster inode lookup blocks or the block device queues are
> full.
>
> Writeback during inode reclaim becomes a little more complex because
> we now have to lock the buffer ourselves, but otherwise this change
> is largely a functional no-op that removes a whole lot of code.
>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>

/This/ looks pretty straightforward. I always wondered about the fact
that the inode item push function would extract a buffer pointer but
then imap_to_bp would replace our pointer...

Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D

> ---
> fs/xfs/xfs_inode.c | 106 ++++++----------------------------------
> fs/xfs/xfs_inode.h | 2 +-
> fs/xfs/xfs_inode_item.c | 51 +++++++------------
> 3 files changed, 32 insertions(+), 127 deletions(-)
>
> diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> index 961eef2ce8c4a..a94528d26328b 100644
> --- a/fs/xfs/xfs_inode.c
> +++ b/fs/xfs/xfs_inode.c
> @@ -3429,7 +3429,18 @@ xfs_rename(
> return error;
> }
>
> -STATIC int
> +/*
> + * Non-blocking flush of dirty inode metadata into the backing buffer.
> + *
> + * The caller must have a reference to the inode and hold the cluster buffer
> + * locked. The function will walk across all the inodes on the cluster buffer it
> + * can find and lock without blocking, and flush them to the cluster buffer.
> + *
> + * On success, the caller must write out the buffer returned in *bp and
> + * release it. On failure, the filesystem will be shut down, the buffer will
> + * have been unlocked and released, and EFSCORRUPTED will be returned.
> + */
> +int
> xfs_iflush_cluster(
> struct xfs_inode *ip,
> struct xfs_buf *bp)
> @@ -3464,8 +3475,6 @@ xfs_iflush_cluster(
>
> for (i = 0; i < nr_found; i++) {
> cip = cilist[i];
> - if (cip == ip)
> - continue;
>
> /*
> * because this is an RCU protected lookup, we could find a
> @@ -3556,99 +3565,11 @@ xfs_iflush_cluster(
> kmem_free(cilist);
> out_put:
> xfs_perag_put(pag);
> - return error;
> -}
> -
> -/*
> - * Flush dirty inode metadata into the backing buffer.
> - *
> - * The caller must have the inode lock and the inode flush lock held. The
> - * inode lock will still be held upon return to the caller, and the inode
> - * flush lock will be released after the inode has reached the disk.
> - *
> - * The caller must write out the buffer returned in *bpp and release it.
> - */
> -int
> -xfs_iflush(
> - struct xfs_inode *ip,
> - struct xfs_buf **bpp)
> -{
> - struct xfs_mount *mp = ip->i_mount;
> - struct xfs_buf *bp = NULL;
> - struct xfs_dinode *dip;
> - int error;
> -
> - XFS_STATS_INC(mp, xs_iflush_count);
> -
> - ASSERT(xfs_isilocked(ip, XFS_ILOCK_EXCL|XFS_ILOCK_SHARED));
> - ASSERT(xfs_isiflocked(ip));
> - ASSERT(ip->i_df.if_format != XFS_DINODE_FMT_BTREE ||
> - ip->i_df.if_nextents > XFS_IFORK_MAXEXT(ip, XFS_DATA_FORK));
> -
> - *bpp = NULL;
> -
> - xfs_iunpin_wait(ip);
> -
> - /*
> - * For stale inodes we cannot rely on the backing buffer remaining
> - * stale in cache for the remaining life of the stale inode and so
> - * xfs_imap_to_bp() below may give us a buffer that no longer contains
> - * inodes below. We have to check this after ensuring the inode is
> - * unpinned so that it is safe to reclaim the stale inode after the
> - * flush call.
> - */
> - if (xfs_iflags_test(ip, XFS_ISTALE)) {
> - xfs_ifunlock(ip);
> - return 0;
> - }
> -
> - /*
> - * Get the buffer containing the on-disk inode. We are doing a try-lock
> - * operation here, so we may get an EAGAIN error. In that case, return
> - * leaving the inode dirty.
> - *
> - * If we get any other error, we effectively have a corruption situation
> - * and we cannot flush the inode. Abort the flush and shut down.
> - */
> - error = xfs_imap_to_bp(mp, NULL, &ip->i_imap, &dip, &bp, XBF_TRYLOCK);
> - if (error == -EAGAIN) {
> - xfs_ifunlock(ip);
> - return error;
> - }
> - if (error)
> - goto abort;
> -
> - /*
> - * If the buffer is pinned then push on the log now so we won't
> - * get stuck waiting in the write for too long.
> - */
> - if (xfs_buf_ispinned(bp))
> - xfs_log_force(mp, 0);
> -
> - /*
> - * Flush the provided inode then attempt to gather others from the
> - * cluster into the write.
> - *
> - * Note: Once we attempt to flush an inode, we must run buffer
> - * completion callbacks on any failure. If this fails, simulate an I/O
> - * failure on the buffer and shut down.
> - */
> - error = xfs_iflush_int(ip, bp);
> - if (!error)
> - error = xfs_iflush_cluster(ip, bp);
> if (error) {
> bp->b_flags |= XBF_ASYNC;
> xfs_buf_ioend_fail(bp);
> - goto shutdown;
> + xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_INCORE);
> }
> -
> - *bpp = bp;
> - return 0;
> -
> -abort:
> - xfs_iflush_abort(ip);
> -shutdown:
> - xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_INCORE);
> return error;
> }
>
> @@ -3667,6 +3588,7 @@ xfs_iflush_int(
> ASSERT(ip->i_df.if_format != XFS_DINODE_FMT_BTREE ||
> ip->i_df.if_nextents > XFS_IFORK_MAXEXT(ip, XFS_DATA_FORK));
> ASSERT(iip != NULL && iip->ili_fields != 0);
> + ASSERT(iip->ili_item.li_buf == bp);
>
> dip = xfs_buf_offset(bp, ip->i_imap.im_boffset);
>
> diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
> index dadcf19458960..d1109eb13ba2e 100644
> --- a/fs/xfs/xfs_inode.h
> +++ b/fs/xfs/xfs_inode.h
> @@ -427,7 +427,7 @@ int xfs_log_force_inode(struct xfs_inode *ip);
> void xfs_iunpin_wait(xfs_inode_t *);
> #define xfs_ipincount(ip) ((unsigned int) atomic_read(&ip->i_pincount))
>
> -int xfs_iflush(struct xfs_inode *, struct xfs_buf **);
> +int xfs_iflush_cluster(struct xfs_inode *, struct xfs_buf *);
> void xfs_lock_two_inodes(struct xfs_inode *ip0, uint ip0_mode,
> struct xfs_inode *ip1, uint ip1_mode);
>
> diff --git a/fs/xfs/xfs_inode_item.c b/fs/xfs/xfs_inode_item.c
> index 7718cfc39eec8..42b4b5fe1e2a9 100644
> --- a/fs/xfs/xfs_inode_item.c
> +++ b/fs/xfs/xfs_inode_item.c
> @@ -504,53 +504,35 @@ xfs_inode_item_push(
> uint rval = XFS_ITEM_SUCCESS;
> int error;
>
> - if (xfs_ipincount(ip) > 0)
> - return XFS_ITEM_PINNED;
> + ASSERT(iip->ili_item.li_buf);
>
> - if (!xfs_ilock_nowait(ip, XFS_ILOCK_SHARED))
> - return XFS_ITEM_LOCKED;
> + if (xfs_ipincount(ip) > 0 || xfs_buf_ispinned(bp) ||
> + (ip->i_flags & XFS_ISTALE))
> + return XFS_ITEM_PINNED;
>
> - /*
> - * Re-check the pincount now that we stabilized the value by
> - * taking the ilock.
> - */
> - if (xfs_ipincount(ip) > 0) {
> - rval = XFS_ITEM_PINNED;
> - goto out_unlock;
> - }
> + /* If the inode is already flush locked, we're already flushing. */
> + if (xfs_isiflocked(ip))
> + return XFS_ITEM_FLUSHING;
>
> - /*
> - * Stale inode items should force out the iclog.
> - */
> - if (ip->i_flags & XFS_ISTALE) {
> - rval = XFS_ITEM_PINNED;
> - goto out_unlock;
> - }
> + if (!xfs_buf_trylock(bp))
> + return XFS_ITEM_LOCKED;
>
> - /*
> - * Someone else is already flushing the inode. Nothing we can do
> - * here but wait for the flush to finish and remove the item from
> - * the AIL.
> - */
> - if (!xfs_iflock_nowait(ip)) {
> - rval = XFS_ITEM_FLUSHING;
> - goto out_unlock;
> + if (bp->b_flags & _XBF_DELWRI_Q) {
> + xfs_buf_unlock(bp);
> + return XFS_ITEM_FLUSHING;
> }
> -
> - ASSERT(iip->ili_fields != 0 || XFS_FORCED_SHUTDOWN(ip->i_mount));
> spin_unlock(&lip->li_ailp->ail_lock);
>
> - error = xfs_iflush(ip, &bp);
> + error = xfs_iflush_cluster(ip, bp);
> if (!error) {
> if (!xfs_buf_delwri_queue(bp, buffer_list))
> rval = XFS_ITEM_FLUSHING;
> - xfs_buf_relse(bp);
> - } else if (error == -EAGAIN)
> + xfs_buf_unlock(bp);
> + } else {
> rval = XFS_ITEM_LOCKED;
> + }
>
> spin_lock(&lip->li_ailp->ail_lock);
> -out_unlock:
> - xfs_iunlock(ip, XFS_ILOCK_SHARED);
> return rval;
> }
>
> @@ -567,6 +549,7 @@ xfs_inode_item_release(
>
> ASSERT(ip->i_itemp != NULL);
> ASSERT(xfs_isilocked(ip, XFS_ILOCK_EXCL));
> + ASSERT(lip->li_buf || !test_bit(XFS_LI_DIRTY, &lip->li_flags));
>
> lock_flags = iip->ili_lock_flags;
> iip->ili_lock_flags = 0;
> --
> 2.26.2.761.g0e0b3e54be
>