ext4: tune mballoc's default group prealloc size for bigalloc file systems (27baebb8) · Commits · 戴 / test

fs/ext4/mballoc.c

+16 −2

Original line number	Diff line number	Diff line
		@@ -126,7 +126,8 @@
		* list. In case of inode preallocation we follow a list of heuristics
		* based on file size. This can be found in ext4_mb_normalize_request. If
		* we are doing a group prealloc we try to normalize the request to
		* sbi->s_mb_group_prealloc. Default value of s_mb_group_prealloc is
		* sbi->s_mb_group_prealloc. The default value of s_mb_group_prealloc is
		* dependent on the cluster size; for non-bigalloc file systems, it is
		* 512 blocks. This can be tuned via
		* /sys/fs/ext4/<partition>/mb_group_prealloc. The value is represented in
		* terms of number of blocks. If we have mounted the file system with -O
		@@ -2473,7 +2474,20 @@ int ext4_mb_init(struct super_block *sb, int needs_recovery)
		sbi->s_mb_stats = MB_DEFAULT_STATS;
		sbi->s_mb_stream_request = MB_DEFAULT_STREAM_THRESHOLD;
		sbi->s_mb_order2_reqs = MB_DEFAULT_ORDER2_REQS;
		sbi->s_mb_group_prealloc = MB_DEFAULT_GROUP_PREALLOC;
		/*
		* The default group preallocation is 512, which for 4k block
		* sizes translates to 2 megabytes. However for bigalloc file
		* systems, this is probably too big (i.e, if the cluster size
		* is 1 megabyte, then group preallocation size becomes half a
		* gigabyte!). As a default, we will keep a two megabyte
		* group pralloc size for cluster sizes up to 64k, and after
		* that, we will force a minimum group preallocation size of
		* 32 clusters. This translates to 8 megs when the cluster
		* size is 256k, and 32 megs when the cluster size is 1 meg,
		* which seems reasonable as a default.
		*/
		sbi->s_mb_group_prealloc = max(MB_DEFAULT_GROUP_PREALLOC >>
		sbi->s_cluster_bits, 32);
		/*
		* If there is a s_stripe > 1, then we set the s_mb_group_prealloc
		* to the lowest multiple of s_stripe which is bigger than

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