[PATCH 2/6] xfs: invert the realtime summary cache

Omar Sandoval
2023-06-20T21:32:27Z

From: Omar Sandoval <osandov@fb.com>

In commit 355e3532132b ("xfs: cache minimum realtime summary level"), I
added a cache of the minimum level of the realtime summary that has any
free extents. However, it turns out that the _maximum_ level is more
useful for upcoming optimizations, and basically equivalent for the
existing usage. So, let's change the meaning of the cache to be the
maximum level + 1, or 0 if there are no free extents.

Signed-off-by: Omar Sandoval <osandov@fb.com>
---
fs/xfs/libxfs/xfs_rtbitmap.c | 6 +++---
fs/xfs/xfs_mount.h | 6 +++---
fs/xfs/xfs_rtalloc.c | 31 +++++++++++++++++++------------
3 files changed, 25 insertions(+), 18 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_rtbitmap.c b/fs/xfs/libxfs/xfs_rtbitmap.c
index 1a832c9a412f..d9493f64adfc 100644
--- a/fs/xfs/libxfs/xfs_rtbitmap.c
+++ b/fs/xfs/libxfs/xfs_rtbitmap.c
@@ -503,10 +503,10 @@ xfs_rtmodify_summary_int(

*sp += delta;
if (mp->m_rsum_cache) {
- if (*sp == 0 && log == mp->m_rsum_cache[bbno])
- mp->m_rsum_cache[bbno]++;
- if (*sp != 0 && log < mp->m_rsum_cache[bbno])
+ if (*sp == 0 && log + 1 == mp->m_rsum_cache[bbno])
mp->m_rsum_cache[bbno] = log;
+ if (*sp != 0 && log >= mp->m_rsum_cache[bbno])
+ mp->m_rsum_cache[bbno] = log + 1;
}
xfs_trans_log_buf(tp, bp, first, first + sizeof(*sp) - 1);
}
diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
index 6c09f89534d3..964541c36730 100644
--- a/fs/xfs/xfs_mount.h
+++ b/fs/xfs/xfs_mount.h
@@ -103,9 +103,9 @@ typedef struct xfs_mount {

/*
* Optional cache of rt summary level per bitmap block with the
- * invariant that m_rsum_cache[bbno] <= the minimum i for which
- * rsum[i][bbno] != 0. Reads and writes are serialized by the rsumip
- * inode lock.
+ * invariant that m_rsum_cache[bbno] > the maximum i for which
+ * rsum[i][bbno] != 0, or 0 if rsum[i][bbno] == 0 for all i.
+ * Reads and writes are serialized by the rsumip inode lock.
*/
uint8_t *m_rsum_cache;
struct xfs_mru_cache *m_filestream; /* per-mount filestream data */
diff --git a/fs/xfs/xfs_rtalloc.c b/fs/xfs/xfs_rtalloc.c
index 61ef13286654..d3c76532d20e 100644
--- a/fs/xfs/xfs_rtalloc.c
+++ b/fs/xfs/xfs_rtalloc.c
@@ -56,14 +56,19 @@ xfs_rtany_summary(
int log; /* loop counter, log2 of ext. size */
xfs_suminfo_t sum; /* summary data */

- /* There are no extents at levels < m_rsum_cache[bbno]. */
- if (mp->m_rsum_cache && low < mp->m_rsum_cache[bbno])
- low = mp->m_rsum_cache[bbno];
+ /* There are no extents at levels >= m_rsum_cache[bbno]. */
+ if (mp->m_rsum_cache) {
+ high = min(high, mp->m_rsum_cache[bbno] - 1);
+ if (low > high) {
+ *stat = 0;
+ return 0;
+ }
+ }

/*
* Loop over logs of extent sizes.
*/
- for (log = low; log <= high; log++) {
+ for (log = high; log >= low; log--) {
/*
* Get one summary datum.
*/
@@ -84,9 +89,9 @@ xfs_rtany_summary(
*/
*stat = 0;
out:
- /* There were no extents at levels < log. */
- if (mp->m_rsum_cache && log > mp->m_rsum_cache[bbno])
- mp->m_rsum_cache[bbno] = log;
+ /* There were no extents at levels > log. */
+ if (mp->m_rsum_cache && log + 1 < mp->m_rsum_cache[bbno])
+ mp->m_rsum_cache[bbno] = log + 1;
return 0;
}

@@ -878,12 +883,14 @@ xfs_alloc_rsum_cache(
xfs_extlen_t rbmblocks) /* number of rt bitmap blocks */
{
/*
- * The rsum cache is initialized to all zeroes, which is trivially a
- * lower bound on the minimum level with any free extents. We can
- * continue without the cache if it couldn't be allocated.
+ * The rsum cache is initialized to the maximum value, which is
+ * trivially an upper bound on the maximum level with any free extents.
+ * We can continue without the cache if it couldn't be allocated.
*/
- mp->m_rsum_cache = kvzalloc(rbmblocks, GFP_KERNEL);
- if (!mp->m_rsum_cache)
+ mp->m_rsum_cache = kvmalloc(rbmblocks, GFP_KERNEL);
+ if (mp->m_rsum_cache)
+ memset(mp->m_rsum_cache, -1, rbmblocks);
+ else
xfs_warn(mp, "could not allocate realtime summary cache");
}

--
2.41.0