[PATCH v5 5/6] xfs: add quota-driven speculative preallocation throttling

Brian Foster
2013-03-18T14:50:17Z

Introduce the need_throttle() and calc_throttle() functions to
independently check whether throttling is required for a particular
dquot and if so, calculate the associated throttling metrics based
on the state of the quota. We use the same general algorithm to
calculate the throttle shift as for global free space with the
exception of using three stages rather than five.

Update xfs_iomap_prealloc_size() to use the smallest available
prealloc size based on each of the constraints and apply the
maximum shift to obtain the throttled preallocation size.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
---
fs/xfs/xfs_iomap.c | 82 ++++++++++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 82 insertions(+), 0 deletions(-)

diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 9072794..0a53085 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -42,6 +42,8 @@
#include "xfs_iomap.h"
#include "xfs_trace.h"
#include "xfs_icache.h"
+#include "xfs_dquot_item.h"
+#include "xfs_dquot.h"

#define XFS_WRITEIO_ALIGN(mp,off) (((off) >> mp->m_writeio_log) \
@@ -366,6 +368,61 @@ xfs_iomap_eof_prealloc_initial_size(
return XFS_B_TO_FSB(mp, offset);
}

+STATIC bool
+xfs_quota_need_throttle(
+ struct xfs_inode *ip,
+ int type,
+ xfs_fsblock_t alloc_blocks)
+{
+ struct xfs_dquot *dq = xfs_inode_dquot(ip, type);
+
+ if (!dq || !xfs_this_quota_on(ip->i_mount, type))
+ return false;
+
+ /* no hi watermark, no throttle */
+ if (!dq->q_prealloc_hi_wmark)
+ return false;
+
+ /* under the lo watermark, no throttle */
+ if (dq->q_res_bcount + alloc_blocks < dq->q_prealloc_lo_wmark)
+ return false;
+
+ return true;
+}
+
+STATIC void
+xfs_quota_calc_throttle(
+ struct xfs_inode *ip,
+ int type,
+ xfs_fsblock_t *qblocks,
+ int *qshift)
+{
+ int64_t freesp;
+ int shift = 0;
+ struct xfs_dquot *dq = xfs_inode_dquot(ip, type);
+
+ /* over hi wmark, squash the prealloc completely */
+ if (dq->q_res_bcount >= dq->q_prealloc_hi_wmark) {
+ *qblocks = 0;
+ return;
+ }
+
+ freesp = dq->q_prealloc_hi_wmark - dq->q_res_bcount;
+ if (freesp < dq->q_low_space[XFS_QLOWSP_5_PCNT]) {
+ shift = 2;
+ if (freesp < dq->q_low_space[XFS_QLOWSP_3_PCNT])
+ shift += 2;
+ if (freesp < dq->q_low_space[XFS_QLOWSP_1_PCNT])
+ shift += 2;
+ }
+
+ /* only overwrite the throttle values if we are more aggressive */
+ if ((freesp >> shift) < (*qblocks >> *qshift)) {
+ *qblocks = freesp;
+ *qshift = shift;
+ }
+}
+
/*
* If we don't have a user specified preallocation size, dynamically increase
* the preallocation size as the size of the file grows. Cap the maximum size
@@ -383,11 +440,14 @@ xfs_iomap_prealloc_size(
xfs_fsblock_t alloc_blocks = 0;
int shift = 0;
int64_t freesp;
+ xfs_fsblock_t qblocks;
+ int qshift = 0;

alloc_blocks = xfs_iomap_eof_prealloc_initial_size(mp, ip, offset,
imap, nimaps);
if (!alloc_blocks)
goto check_writeio;
+ qblocks = alloc_blocks;

/*
* MAXEXTLEN is not a power of two value but we round the prealloc down
@@ -412,6 +472,28 @@ xfs_iomap_prealloc_size(
if (freesp < mp->m_low_space[XFS_LOWSP_1_PCNT])
shift++;
}
+
+ /*
+ * Check each quota to cap the prealloc size and provide a shift
+ * value to throttle with.
+ */
+ if (xfs_quota_need_throttle(ip, XFS_DQ_USER, alloc_blocks))
+ xfs_quota_calc_throttle(ip, XFS_DQ_USER, &qblocks, &qshift);
+ if (xfs_quota_need_throttle(ip, XFS_DQ_GROUP, alloc_blocks))
+ xfs_quota_calc_throttle(ip, XFS_DQ_GROUP, &qblocks, &qshift);
+ if (xfs_quota_need_throttle(ip, XFS_DQ_PROJ, alloc_blocks))
+ xfs_quota_calc_throttle(ip, XFS_DQ_PROJ, &qblocks, &qshift);
+
+ /*
+ * The final prealloc size is set to the minimum of free space available
+ * in each of the quotas and the overall filesystem.
+ *
+ * The shift throttle value is set to the maximum value as determined by
+ * the global low free space values and per-quota low free space values.
+ */
+ alloc_blocks = MIN(alloc_blocks, qblocks);
+ shift = MAX(shift, qshift);
+
if (shift)
alloc_blocks >>= shift;
/*