ext4: allocate stripe-multiple IOs on stripe boundaries (506bf2d8) · Commits · 戴 / test

For some reason, today mballoc only allocates IOs which are exactly stripe-sized on a stripe boundary. If you have a multiple (say, a 128k IO on a 64k stripe) you may end up unaligned. It seems to me that a simple change to align stripe-multiple IOs on stripe boundaries would be a very good idea, unless this breaks some other mballoc heuristic for some reason... Reported-by:

Mike Snitzer <snitzer@redhat.com> Signed-off-by:

Eric Sandeen <sandeen@redhat.com> Signed-off-by:

"Theodore Ts'o" <tytso@mit.edu>

fs/ext4/mballoc.c

+3 −4

Original line number	Diff line number	Diff line
		@@ -1822,8 +1822,7 @@ void ext4_mb_complex_scan_group(struct ext4_allocation_context *ac,

		/*
		* This is a special case for storages like raid5
		* we try to find stripe-aligned chunks for stripe-size requests
		* XXX should do so at least for multiples of stripe size as well
		* we try to find stripe-aligned chunks for stripe-size-multiple requests
		*/
		static noinline_for_stack
		void ext4_mb_scan_aligned(struct ext4_allocation_context *ac,
		@@ -2092,8 +2091,8 @@ repeat:
		ac->ac_groups_scanned++;
		if (cr == 0)
		ext4_mb_simple_scan_group(ac, &e4b);
		else if (cr == 1 &&
		ac->ac_g_ex.fe_len == sbi->s_stripe)
		else if (cr == 1 && sbi->s_stripe &&
		!(ac->ac_g_ex.fe_len % sbi->s_stripe))
		ext4_mb_scan_aligned(ac, &e4b);
		else
		ext4_mb_complex_scan_group(ac, &e4b);

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