From 4a69aecbfb30a3fc85bf8028386c047d5607a97a Mon Sep 17 00:00:00 2001 From: Lukas Czerner Date: Wed, 3 Nov 2021 15:51:22 +0100 Subject: ext4: allow to change s_last_trim_minblks via sysfs Ext4 has an optimization mechanism for batched disacrd (FITRIM) that should help speed up subsequent calls of FITRIM ioctl by skipping the groups that were previously trimmed. However because the FITRIM allows to set the minimum size of an extent to trim, ext4 stores the last minimum extent size and only avoids trimming the group if it was previously trimmed with minimum extent size equal to, or smaller than the current call. There is currently no way to bypass the optimization without umount/mount cycle. This becomes a problem when the file system is live migrated to a different storage, because the optimization will prevent possibly useful discard calls to the storage. Fix it by exporting the s_last_trim_minblks via sysfs interface which will allow us to set the minimum size to the number of blocks larger than subsequent FITRIM call, effectively bypassing the optimization. By setting the s_last_trim_minblks to ULONG_MAX the optimization will be effectively cleared regardless of the previous state, or file system configuration. For example: getconf ULONG_MAX > /sys/fs/ext4/dm-1/last_trim_minblks Signed-off-by: Lukas Czerner Reported-by: Laurent GUERBY Reviewed-by: Andreas Dilger Link: https://lore.kernel.org/r/20211103145122.17338-2-lczerner@redhat.com Signed-off-by: Theodore Ts'o --- fs/ext4/sysfs.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'fs') diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c index 2a4ae3d10571..f61e65ae27d8 100644 --- a/fs/ext4/sysfs.c +++ b/fs/ext4/sysfs.c @@ -245,6 +245,7 @@ EXT4_ATTR(last_error_time, 0444, last_error_time); EXT4_ATTR(journal_task, 0444, journal_task); EXT4_RW_ATTR_SBI_UI(mb_prefetch, s_mb_prefetch); EXT4_RW_ATTR_SBI_UI(mb_prefetch_limit, s_mb_prefetch_limit); +EXT4_RW_ATTR_SBI_UL(last_trim_minblks, s_last_trim_minblks); static unsigned int old_bump_val = 128; EXT4_ATTR_PTR(max_writeback_mb_bump, 0444, pointer_ui, &old_bump_val); @@ -295,6 +296,7 @@ static struct attribute *ext4_attrs[] = { #endif ATTR_LIST(mb_prefetch), ATTR_LIST(mb_prefetch_limit), + ATTR_LIST(last_trim_minblks), NULL, }; ATTRIBUTE_GROUPS(ext4); -- cgit v1.2.3