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microzap: set hard upper limit of 1M #16888

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microzap: set hard upper limit of 1M #16888

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18 changes: 15 additions & 3 deletions module/zfs/zap_micro.c
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Original file line number Diff line number Diff line change
Expand Up @@ -54,14 +54,25 @@
* machinery to understand not to try to split a microzap block).
*
* If large_microzap is enabled, this value will be clamped to
* spa_maxblocksize(). If not, it will be clamped to SPA_OLD_MAXBLOCKSIZE.
* spa_maxblocksize(), up to 1M. If not, it will be clamped to
* SPA_OLD_MAXBLOCKSIZE.
*/
static int zap_micro_max_size = SPA_OLD_MAXBLOCKSIZE;

/*
* The 1M upper limit is necessary because the count of chunks in a microzap
* block is stored as a uint16_t (mze_chunkid). Each chunk is 64 bytes, and the
* first is used to store a header, so there are 32767 usable chunks, which is
* just under 2M. 1M is the largest power-2-rounded block size under 2M, so we
* must set the limit there.
*/
#define MZAP_MAX_SIZE (1048576)

uint64_t
zap_get_micro_max_size(spa_t *spa)
{
uint64_t maxsz = P2ROUNDUP(zap_micro_max_size, SPA_MINBLOCKSIZE);
uint64_t maxsz = MIN(MZAP_MAX_SIZE,
P2ROUNDUP(zap_micro_max_size, SPA_MINBLOCKSIZE));
if (maxsz <= SPA_OLD_MAXBLOCKSIZE)
return (maxsz);
if (spa_feature_is_enabled(spa, SPA_FEATURE_LARGE_MICROZAP))
Expand Down Expand Up @@ -2031,5 +2042,6 @@ EXPORT_SYMBOL(zap_cursor_init_serialized);
EXPORT_SYMBOL(zap_get_stats);

ZFS_MODULE_PARAM(zfs, , zap_micro_max_size, INT, ZMOD_RW,
"Maximum micro ZAP size, before converting to a fat ZAP, in bytes");
"Maximum micro ZAP size before converting to a fat ZAP, "
"in bytes (max 1M)");
#endif
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