From 0ce6300feca082a866a58fa1f4f9af47a450c41c Mon Sep 17 00:00:00 2001 From: Filipe Manana Date: Fri, 17 Oct 2025 16:10:04 +0100 Subject: [PATCH] btrfs: avoid used space computation when reserving space In __reserve_bytes() we have 3 repeated calls to btrfs_space_info_used(), one early on as soon as take the space_info's spinlock, another one when we call btrfs_can_overcommit(), which calls btrfs_space_info_used() again, and a final one when we are reserving for a flush emergency. During all these calls we are holding the space_info's spinlock, which is heavily used by the space reservation and flushing code, so it's desirable to make the critical sections as short as possible. So make this more efficient by: 1) Instead of calling btrfs_can_overcommit() call the new variant can_overcommit() which takes the space_info's used space as an argument and pass the value we already computed and have in the 'used' variable; 2) Instead of calling btrfs_space_info_used() with its second argument as false when we are doing a flush emergency, decrement the space_info's bytes_may_use counter from the 'used' variable, as the difference between passing true or false as the second argument to btrfs_space_info_used() is whether or not to include the space_info's bytes_may_use counter in the computation. Reviewed-by: Johannes Thumshirn Signed-off-by: Filipe Manana Signed-off-by: David Sterba --- fs/btrfs/space-info.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/fs/btrfs/space-info.c b/fs/btrfs/space-info.c index f5ff51680f412..6c2769044b552 100644 --- a/fs/btrfs/space-info.c +++ b/fs/btrfs/space-info.c @@ -1783,7 +1783,7 @@ static int __reserve_bytes(struct btrfs_space_info *space_info, u64 orig_bytes, */ if (!pending_tickets && ((used + orig_bytes <= space_info->total_bytes) || - btrfs_can_overcommit(space_info, orig_bytes, flush))) { + can_overcommit(space_info, used, orig_bytes, flush))) { btrfs_space_info_update_bytes_may_use(space_info, orig_bytes); ret = 0; } @@ -1794,7 +1794,7 @@ static int __reserve_bytes(struct btrfs_space_info *space_info, u64 orig_bytes, * left to allocate for the block. */ if (ret && unlikely(flush == BTRFS_RESERVE_FLUSH_EMERGENCY)) { - used = btrfs_space_info_used(space_info, false); + used -= space_info->bytes_may_use; if (used + orig_bytes <= space_info->total_bytes) { btrfs_space_info_update_bytes_may_use(space_info, orig_bytes); ret = 0; -- 2.47.3