Re: [PATCH 22/26] xfs: track reclaimable inodes using a LRU list

Brian Foster
2019-10-14T13:07:13Z

On Wed, Oct 09, 2019 at 02:21:20PM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> Now that we don't do IO from the inode reclaim code, there is no
> need to optimise inode scanning order for optimal IO
> characteristics. The AIL takes care of that for us, so now reclaim
> can focus on selecting the best inodes to reclaim.
>
> Hence we can change the inode reclaim algorithm to a real LRU and
> remove the need to use the radix tree to track and walk inodes under
> reclaim. This frees up a radix tree bit and simplifies the code that
> marks inodes are reclaim candidates. It also simplifies the reclaim
> code - we don't need batching anymore and all the reclaim logic
> can be added to the LRU isolation callback.
>
> Further, we get node aware reclaim at the xfs_inode level, which
> should help the per-node reclaim code free relevant inodes faster.
>
> We can re-use the VFS inode lru pointers - once the inode has been
> reclaimed from the VFS, we can use these pointers ourselves. Hence
> we don't need to grow the inode to change the way we index
> reclaimable inodes.
>
> Start by adding the list_lru tracking in parallel with the existing
> reclaim code. This makes it easier to see the LRU infrastructure
> separate to the reclaim algorithm changes. Especially the locking
> order, which is ip->i_flags_lock -> list_lru lock.
>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---

Looks reasonable:

Reviewed-by: Brian Foster <bfoster@redhat.com>

> fs/xfs/xfs_icache.c | 32 ++++++++------------------------
> fs/xfs/xfs_icache.h | 1 -
> fs/xfs/xfs_mount.h | 1 +
> fs/xfs/xfs_super.c | 29 ++++++++++++++++++++++-------
> 4 files changed, 31 insertions(+), 32 deletions(-)
>
> diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
> index 39c56200f1ce..06fdaa746674 100644
> --- a/fs/xfs/xfs_icache.c
> +++ b/fs/xfs/xfs_icache.c
> @@ -198,6 +198,8 @@ xfs_inode_set_reclaim_tag(
> xfs_perag_set_reclaim_tag(pag);
> __xfs_iflags_set(ip, XFS_IRECLAIMABLE);
>
> + list_lru_add(&mp->m_inode_lru, &VFS_I(ip)->i_lru);
> +
> spin_unlock(&ip->i_flags_lock);
> spin_unlock(&pag->pag_ici_lock);
> xfs_perag_put(pag);
> @@ -370,12 +372,10 @@ xfs_iget_cache_hit(
>
> /*
> * We need to set XFS_IRECLAIM to prevent xfs_reclaim_inode
> - * from stomping over us while we recycle the inode. We can't
> - * clear the radix tree reclaimable tag yet as it requires
> - * pag_ici_lock to be held exclusive.
> + * from stomping over us while we recycle the inode. Remove it
> + * from the LRU straight away so we can re-init the VFS inode.
> */
> ip->i_flags |= XFS_IRECLAIM;
> -
> spin_unlock(&ip->i_flags_lock);
> rcu_read_unlock();
>
> @@ -407,6 +407,7 @@ xfs_iget_cache_hit(
> */
> ip->i_flags &= ~XFS_IRECLAIM_RESET_FLAGS;
> ip->i_flags |= XFS_INEW;
> + list_lru_del(&mp->m_inode_lru, &inode->i_lru);
> xfs_inode_clear_reclaim_tag(pag, ip->i_ino);
> inode->i_state = I_NEW;
> ip->i_sick = 0;
> @@ -1138,6 +1139,9 @@ xfs_reclaim_inode(
> ino = ip->i_ino; /* for radix_tree_delete */
> ip->i_flags = XFS_IRECLAIM;
> ip->i_ino = 0;
> +
> + /* XXX: temporary until lru based reclaim */
> + list_lru_del(&pag->pag_mount->m_inode_lru, &VFS_I(ip)->i_lru);
> spin_unlock(&ip->i_flags_lock);
>
> xfs_iunlock(ip, XFS_ILOCK_EXCL);
> @@ -1329,26 +1333,6 @@ xfs_reclaim_inodes_nr(
> return xfs_reclaim_inodes_ag(mp, sync_mode, nr_to_scan);
> }
>
> -/*
> - * Return the number of reclaimable inodes in the filesystem for
> - * the shrinker to determine how much to reclaim.
> - */
> -int
> -xfs_reclaim_inodes_count(
> - struct xfs_mount *mp)
> -{
> - struct xfs_perag *pag;
> - xfs_agnumber_t ag = 0;
> - int reclaimable = 0;
> -
> - while ((pag = xfs_perag_get_tag(mp, ag, XFS_ICI_RECLAIM_TAG))) {
> - ag = pag->pag_agno + 1;
> - reclaimable += pag->pag_ici_reclaimable;
> - xfs_perag_put(pag);
> - }
> - return reclaimable;
> -}
> -
> STATIC int
> xfs_inode_match_id(
> struct xfs_inode *ip,
> diff --git a/fs/xfs/xfs_icache.h b/fs/xfs/xfs_icache.h
> index 1c9b9edb2986..0ab08b58cd45 100644
> --- a/fs/xfs/xfs_icache.h
> +++ b/fs/xfs/xfs_icache.h
> @@ -50,7 +50,6 @@ struct xfs_inode * xfs_inode_alloc(struct xfs_mount *mp, xfs_ino_t ino);
> void xfs_inode_free(struct xfs_inode *ip);
>
> void xfs_reclaim_inodes(struct xfs_mount *mp);
> -int xfs_reclaim_inodes_count(struct xfs_mount *mp);
> long xfs_reclaim_inodes_nr(struct xfs_mount *mp, int nr_to_scan);
>
> void xfs_inode_set_reclaim_tag(struct xfs_inode *ip);
> diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
> index f0cc952ad527..f1e4c2eae984 100644
> --- a/fs/xfs/xfs_mount.h
> +++ b/fs/xfs/xfs_mount.h
> @@ -75,6 +75,7 @@ typedef struct xfs_mount {
> uint8_t m_rt_sick;
>
> struct xfs_ail *m_ail; /* fs active log item list */
> + struct list_lru m_inode_lru;
>
> struct xfs_sb m_sb; /* copy of fs superblock */
> spinlock_t m_sb_lock; /* sb counter lock */
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index d0619bf02a5d..01f08706a3fb 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -920,28 +920,31 @@ xfs_fs_destroy_inode(
> struct inode *inode)
> {
> struct xfs_inode *ip = XFS_I(inode);
> + struct xfs_mount *mp = ip->i_mount;
>
> trace_xfs_destroy_inode(ip);
>
> ASSERT(!rwsem_is_locked(&inode->i_rwsem));
> - XFS_STATS_INC(ip->i_mount, vn_rele);
> - XFS_STATS_INC(ip->i_mount, vn_remove);
> + XFS_STATS_INC(mp, vn_rele);
> + XFS_STATS_INC(mp, vn_remove);
>
> xfs_inactive(ip);
>
> - if (!XFS_FORCED_SHUTDOWN(ip->i_mount) && ip->i_delayed_blks) {
> + if (!XFS_FORCED_SHUTDOWN(mp) && ip->i_delayed_blks) {
> xfs_check_delalloc(ip, XFS_DATA_FORK);
> xfs_check_delalloc(ip, XFS_COW_FORK);
> ASSERT(0);
> }
>
> - XFS_STATS_INC(ip->i_mount, vn_reclaim);
> + XFS_STATS_INC(mp, vn_reclaim);
>
> /*
> * We should never get here with one of the reclaim flags already set.
> */
> - ASSERT_ALWAYS(!xfs_iflags_test(ip, XFS_IRECLAIMABLE));
> - ASSERT_ALWAYS(!xfs_iflags_test(ip, XFS_IRECLAIM));
> + spin_lock(&ip->i_flags_lock);
> + ASSERT_ALWAYS(!__xfs_iflags_test(ip, XFS_IRECLAIMABLE));
> + ASSERT_ALWAYS(!__xfs_iflags_test(ip, XFS_IRECLAIM));
> + spin_unlock(&ip->i_flags_lock);
>
> /*
> * We always use background reclaim here because even if the
> @@ -1542,6 +1545,15 @@ xfs_mount_alloc(
> if (!mp)
> return NULL;
>
> + /*
> + * The inode lru needs to be associated with the superblock shrinker,
> + * and like the rest of the superblock shrinker, it's memcg aware.
> + */
> + if (list_lru_init_memcg(&mp->m_inode_lru, &sb->s_shrink)) {
> + kfree(mp);
> + return NULL;
> + }
> +
> mp->m_super = sb;
> spin_lock_init(&mp->m_sb_lock);
> spin_lock_init(&mp->m_agirotor_lock);
> @@ -1751,6 +1763,7 @@ xfs_fs_fill_super(
> out_free_fsname:
> sb->s_fs_info = NULL;
> xfs_free_fsname(mp);
> + list_lru_destroy(&mp->m_inode_lru);
> kfree(mp);
> out:
> return error;
> @@ -1783,6 +1796,7 @@ xfs_fs_put_super(
>
> sb->s_fs_info = NULL;
> xfs_free_fsname(mp);
> + list_lru_destroy(&mp->m_inode_lru);
> kfree(mp);
> }
>
> @@ -1804,7 +1818,8 @@ xfs_fs_nr_cached_objects(
> /* Paranoia: catch incorrect calls during mount setup or teardown */
> if (WARN_ON_ONCE(!sb->s_fs_info))
> return 0;
> - return xfs_reclaim_inodes_count(XFS_M(sb));
> +
> + return list_lru_shrink_count(&XFS_M(sb)->m_inode_lru, sc);
> }
>
> static long
> --
> 2.23.0.rc1
>