Skip to content

Commit

Permalink
xfs: track AGs with reclaimable inodes in per-ag radix tree
Browse files Browse the repository at this point in the history
https://bugzilla.kernel.org/show_bug.cgi?id=16348

When the filesystem grows to a large number of allocation groups,
the summing of recalimable inodes gets expensive. In many cases,
most AGs won't have any reclaimable inodes and so we are wasting CPU
time aggregating over these AGs. This is particularly important for
the inode shrinker that gets called frequently under memory
pressure.

To avoid the overhead, track AGs with reclaimable inodes in the
per-ag radix tree so that we can find all the AGs with reclaimable
inodes via a simple gang tag lookup. This involves setting the tag
when the first reclaimable inode is tracked in the AG, and removing
the tag when the last reclaimable inode is removed from the tree.
Then the summation process becomes a loop walking the radix tree
summing AGs with the reclaim tag set.

This significantly reduces the overhead of scanning - a 6400 AG
filesystea now only uses about 25% of a cpu in kswapd while slab
reclaim progresses instead of being permanently stuck at 100% CPU
and making little progress. Clean filesystems filesystems will see
no overhead and the overhead only increases linearly with the number
of dirty AGs.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
  • Loading branch information
Dave Chinner authored and Dave Chinner committed Jul 19, 2010
1 parent 70e60ce commit 16fd536
Show file tree
Hide file tree
Showing 2 changed files with 67 additions and 7 deletions.
71 changes: 64 additions & 7 deletions fs/xfs/linux-2.6/xfs_sync.c
Original file line number Diff line number Diff line change
Expand Up @@ -144,6 +144,41 @@ xfs_inode_ag_walk(
return last_error;
}

/*
* Select the next per-ag structure to iterate during the walk. The reclaim
* walk is optimised only to walk AGs with reclaimable inodes in them.
*/
static struct xfs_perag *
xfs_inode_ag_iter_next_pag(
struct xfs_mount *mp,
xfs_agnumber_t *first,
int tag)
{
struct xfs_perag *pag = NULL;

if (tag == XFS_ICI_RECLAIM_TAG) {
int found;
int ref;

spin_lock(&mp->m_perag_lock);
found = radix_tree_gang_lookup_tag(&mp->m_perag_tree,
(void **)&pag, *first, 1, tag);
if (found <= 0) {
spin_unlock(&mp->m_perag_lock);
return NULL;
}
*first = pag->pag_agno + 1;
/* open coded pag reference increment */
ref = atomic_inc_return(&pag->pag_ref);
spin_unlock(&mp->m_perag_lock);
trace_xfs_perag_get_reclaim(mp, pag->pag_agno, ref, _RET_IP_);
} else {
pag = xfs_perag_get(mp, *first);
(*first)++;
}
return pag;
}

int
xfs_inode_ag_iterator(
struct xfs_mount *mp,
Expand All @@ -154,16 +189,15 @@ xfs_inode_ag_iterator(
int exclusive,
int *nr_to_scan)
{
struct xfs_perag *pag;
int error = 0;
int last_error = 0;
xfs_agnumber_t ag;
int nr;

nr = nr_to_scan ? *nr_to_scan : INT_MAX;
for (ag = 0; ag < mp->m_sb.sb_agcount; ag++) {
struct xfs_perag *pag;

pag = xfs_perag_get(mp, ag);
ag = 0;
while ((pag = xfs_inode_ag_iter_next_pag(mp, &ag, tag))) {
error = xfs_inode_ag_walk(mp, pag, execute, flags, tag,
exclusive, &nr);
xfs_perag_put(pag);
Expand Down Expand Up @@ -640,6 +674,17 @@ __xfs_inode_set_reclaim_tag(
radix_tree_tag_set(&pag->pag_ici_root,
XFS_INO_TO_AGINO(ip->i_mount, ip->i_ino),
XFS_ICI_RECLAIM_TAG);

if (!pag->pag_ici_reclaimable) {
/* propagate the reclaim tag up into the perag radix tree */
spin_lock(&ip->i_mount->m_perag_lock);
radix_tree_tag_set(&ip->i_mount->m_perag_tree,
XFS_INO_TO_AGNO(ip->i_mount, ip->i_ino),
XFS_ICI_RECLAIM_TAG);
spin_unlock(&ip->i_mount->m_perag_lock);
trace_xfs_perag_set_reclaim(ip->i_mount, pag->pag_agno,
-1, _RET_IP_);
}
pag->pag_ici_reclaimable++;
}

Expand Down Expand Up @@ -674,6 +719,16 @@ __xfs_inode_clear_reclaim_tag(
radix_tree_tag_clear(&pag->pag_ici_root,
XFS_INO_TO_AGINO(mp, ip->i_ino), XFS_ICI_RECLAIM_TAG);
pag->pag_ici_reclaimable--;
if (!pag->pag_ici_reclaimable) {
/* clear the reclaim tag from the perag radix tree */
spin_lock(&ip->i_mount->m_perag_lock);
radix_tree_tag_clear(&ip->i_mount->m_perag_tree,
XFS_INO_TO_AGNO(ip->i_mount, ip->i_ino),
XFS_ICI_RECLAIM_TAG);
spin_unlock(&ip->i_mount->m_perag_lock);
trace_xfs_perag_clear_reclaim(ip->i_mount, pag->pag_agno,
-1, _RET_IP_);
}
}

/*
Expand Down Expand Up @@ -838,7 +893,7 @@ xfs_reclaim_inode_shrink(
struct xfs_mount *mp;
struct xfs_perag *pag;
xfs_agnumber_t ag;
int reclaimable = 0;
int reclaimable;

mp = container_of(shrink, struct xfs_mount, m_inode_shrink);
if (nr_to_scan) {
Expand All @@ -852,8 +907,10 @@ xfs_reclaim_inode_shrink(
return -1;
}

for (ag = 0; ag < mp->m_sb.sb_agcount; ag++) {
pag = xfs_perag_get(mp, ag);
reclaimable = 0;
ag = 0;
while ((pag = xfs_inode_ag_iter_next_pag(mp, &ag,
XFS_ICI_RECLAIM_TAG))) {
reclaimable += pag->pag_ici_reclaimable;
xfs_perag_put(pag);
}
Expand Down
3 changes: 3 additions & 0 deletions fs/xfs/linux-2.6/xfs_trace.h
Original file line number Diff line number Diff line change
Expand Up @@ -124,7 +124,10 @@ DEFINE_EVENT(xfs_perag_class, name, \
unsigned long caller_ip), \
TP_ARGS(mp, agno, refcount, caller_ip))
DEFINE_PERAG_REF_EVENT(xfs_perag_get);
DEFINE_PERAG_REF_EVENT(xfs_perag_get_reclaim);
DEFINE_PERAG_REF_EVENT(xfs_perag_put);
DEFINE_PERAG_REF_EVENT(xfs_perag_set_reclaim);
DEFINE_PERAG_REF_EVENT(xfs_perag_clear_reclaim);

TRACE_EVENT(xfs_attr_list_node_descend,
TP_PROTO(struct xfs_attr_list_context *ctx,
Expand Down

0 comments on commit 16fd536

Please sign in to comment.