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Ramping up data preallocation

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Ramps up data preallocation based on the number of online
blocks. This results in a simple 2<<n block allocation pattern
until n=11 (2048) - the default value of data_prealloc_blocks.

Signed-off-by: Auke Kok <auke.kok@versity.com>
This commit is contained in:
Auke Kok
2026-03-25 13:53:29 -07:00
parent fc0fc1427f
commit e632e888b3
2 changed files with 24 additions and 6 deletions
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18
kmod/src/data.c
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@@ -384,6 +384,12 @@ static inline u64 ext_last(struct scoutfs_extent *ext)
* This can waste a lot of space for small or sparse files but is
* reasonable when a file population is known to be large and dense but
* known to be written with non-streaming write patterns.
*
* In either strategy, preallocation ramps up proportionally with the
* file's online block count rather than jumping to the full prealloc
* size. This avoids overallocation for small files in mixed-size
* workloads while still allowing large files to benefit from full
* preallocation.
*/
static int alloc_block(struct super_block *sb, struct inode *inode,
struct scoutfs_extent *ext, u64 iblock,
@@ -400,6 +406,7 @@ static int alloc_block(struct super_block *sb, struct inode *inode,
struct scoutfs_extent found;
struct scoutfs_extent pre = {0,};
bool undo_pre = false;
bool have_onoff = false;
u64 blkno = 0;
u64 online;
u64 offline;
@@ -445,6 +452,7 @@ static int alloc_block(struct super_block *sb, struct inode *inode,
* blocks.
*/
scoutfs_inode_get_onoff(inode, &online, &offline);
have_onoff = true;
if (iblock > 1 && iblock == online) {
ret = scoutfs_ext_next(sb, &data_ext_ops, &args,
iblock, 1, &found);
@@ -491,6 +499,16 @@ static int alloc_block(struct super_block *sb, struct inode *inode,
/* overall prealloc limit */
count = min_t(u64, count, opts.data_prealloc_blocks);
/*
* Ramp preallocation up proportionally with the file's online
* block count rather than jumping to the full prealloc size.
*/
if (!ext->len) {
if (!have_onoff)
scoutfs_inode_get_onoff(inode, &online, &offline);
count = max_t(u64, 1, min(count, online));
}
ret = scoutfs_alloc_data(sb, datinf->alloc, datinf->wri,
&datinf->dalloc, count, &blkno, &count);
if (ret < 0)

12
tests/golden/data-prealloc
View File

@@ -8,10 +8,10 @@
/mnt/test/test/data-prealloc/file-1: extents: 32
/mnt/test/test/data-prealloc/file-2: extents: 32
== any writes to region prealloc get full extents
/mnt/test/test/data-prealloc/file-1: extents: 4
/mnt/test/test/data-prealloc/file-2: extents: 4
/mnt/test/test/data-prealloc/file-1: extents: 4
/mnt/test/test/data-prealloc/file-2: extents: 4
/mnt/test/test/data-prealloc/file-1: extents: 8
/mnt/test/test/data-prealloc/file-2: extents: 8
/mnt/test/test/data-prealloc/file-1: extents: 8
/mnt/test/test/data-prealloc/file-2: extents: 8
== streaming offline writes get full extents either way
/mnt/test/test/data-prealloc/file-1: extents: 4
/mnt/test/test/data-prealloc/file-2: extents: 4
@@ -20,8 +20,8 @@
== goofy preallocation amounts work
/mnt/test/test/data-prealloc/file-1: extents: 6
/mnt/test/test/data-prealloc/file-2: extents: 6
/mnt/test/test/data-prealloc/file-1: extents: 6
/mnt/test/test/data-prealloc/file-2: extents: 6
/mnt/test/test/data-prealloc/file-1: extents: 10
/mnt/test/test/data-prealloc/file-2: extents: 10
/mnt/test/test/data-prealloc/file-1: extents: 3
/mnt/test/test/data-prealloc/file-2: extents: 3
== block writes into region allocs hole