From 2e294c60497f29ab8791f4b99f348b22d70dd3c3 Mon Sep 17 00:00:00 2001 From: Josef Bacik Date: Fri, 9 Oct 2020 09:28:26 -0400 Subject: btrfs: simplify the logic in need_preemptive_flushing A lot of this was added all in one go with no explanation, and is a bit unwieldy and confusing. Simplify the logic to start preemptive flushing if we've reserved more than half of our available free space. Reviewed-by: Nikolay Borisov Signed-off-by: Josef Bacik Signed-off-by: David Sterba --- fs/btrfs/space-info.c | 73 +++++++++++++++++++++++++++++++++------------------ 1 file changed, 48 insertions(+), 25 deletions(-) (limited to 'fs/btrfs/space-info.c') diff --git a/fs/btrfs/space-info.c b/fs/btrfs/space-info.c index 636a42620b11..9befd22a2316 100644 --- a/fs/btrfs/space-info.c +++ b/fs/btrfs/space-info.c @@ -786,11 +786,11 @@ btrfs_calc_reclaim_metadata_size(struct btrfs_fs_info *fs_info, } static bool need_preemptive_reclaim(struct btrfs_fs_info *fs_info, - struct btrfs_space_info *space_info, - u64 used) + struct btrfs_space_info *space_info) { + u64 ordered, delalloc; u64 thresh = div_factor_fine(space_info->total_bytes, 98); - u64 to_reclaim, expected; + u64 used; /* If we're just plain full then async reclaim just slows us down. */ if ((space_info->bytes_used + space_info->bytes_reserved) >= thresh) @@ -803,26 +803,52 @@ static bool need_preemptive_reclaim(struct btrfs_fs_info *fs_info, if (space_info->reclaim_size) return false; - to_reclaim = min_t(u64, num_online_cpus() * SZ_1M, SZ_16M); - if (btrfs_can_overcommit(fs_info, space_info, to_reclaim, - BTRFS_RESERVE_FLUSH_ALL)) - return false; + /* + * If we have over half of the free space occupied by reservations or + * pinned then we want to start flushing. + * + * We do not do the traditional thing here, which is to say + * + * if (used >= ((total_bytes + avail) / 2)) + * return 1; + * + * because this doesn't quite work how we want. If we had more than 50% + * of the space_info used by bytes_used and we had 0 available we'd just + * constantly run the background flusher. Instead we want it to kick in + * if our reclaimable space exceeds 50% of our available free space. + */ + thresh = calc_available_free_space(fs_info, space_info, + BTRFS_RESERVE_FLUSH_ALL); + thresh += (space_info->total_bytes - space_info->bytes_used - + space_info->bytes_reserved - space_info->bytes_readonly); + thresh >>= 1; - used = btrfs_space_info_used(space_info, true); - if (btrfs_can_overcommit(fs_info, space_info, SZ_1M, - BTRFS_RESERVE_FLUSH_ALL)) - expected = div_factor_fine(space_info->total_bytes, 95); - else - expected = div_factor_fine(space_info->total_bytes, 90); + used = space_info->bytes_pinned; - if (used > expected) - to_reclaim = used - expected; + /* + * If we have more ordered bytes than delalloc bytes then we're either + * doing a lot of DIO, or we simply don't have a lot of delalloc waiting + * around. Preemptive flushing is only useful in that it can free up + * space before tickets need to wait for things to finish. In the case + * of ordered extents, preemptively waiting on ordered extents gets us + * nothing, if our reservations are tied up in ordered extents we'll + * simply have to slow down writers by forcing them to wait on ordered + * extents. + * + * In the case that ordered is larger than delalloc, only include the + * block reserves that we would actually be able to directly reclaim + * from. In this case if we're heavy on metadata operations this will + * clearly be heavy enough to warrant preemptive flushing. In the case + * of heavy DIO or ordered reservations, preemptive flushing will just + * waste time and cause us to slow down. + */ + ordered = percpu_counter_sum_positive(&fs_info->ordered_bytes); + delalloc = percpu_counter_sum_positive(&fs_info->delalloc_bytes); + if (ordered >= delalloc) + used += fs_info->delayed_refs_rsv.reserved + + fs_info->delayed_block_rsv.reserved; else - to_reclaim = 0; - to_reclaim = min(to_reclaim, space_info->bytes_may_use + - space_info->bytes_reserved); - if (!to_reclaim) - return false; + used += space_info->bytes_may_use; return (used >= thresh && !btrfs_fs_closing(fs_info) && !test_bit(BTRFS_FS_STATE_REMOUNTING, &fs_info->fs_state)); @@ -1019,7 +1045,6 @@ static void btrfs_preempt_reclaim_metadata_space(struct work_struct *work) struct btrfs_block_rsv *delayed_refs_rsv; struct btrfs_block_rsv *global_rsv; struct btrfs_block_rsv *trans_rsv; - u64 used; fs_info = container_of(work, struct btrfs_fs_info, preempt_reclaim_work); @@ -1030,8 +1055,7 @@ static void btrfs_preempt_reclaim_metadata_space(struct work_struct *work) trans_rsv = &fs_info->trans_block_rsv; spin_lock(&space_info->lock); - used = btrfs_space_info_used(space_info, true); - while (need_preemptive_reclaim(fs_info, space_info, used)) { + while (need_preemptive_reclaim(fs_info, space_info)) { enum btrfs_flush_state flush; u64 delalloc_size = 0; u64 to_reclaim, block_rsv_size; @@ -1092,7 +1116,6 @@ static void btrfs_preempt_reclaim_metadata_space(struct work_struct *work) flush_space(fs_info, space_info, to_reclaim, flush); cond_resched(); spin_lock(&space_info->lock); - used = btrfs_space_info_used(space_info, true); } spin_unlock(&space_info->lock); } @@ -1511,7 +1534,7 @@ static int __reserve_bytes(struct btrfs_fs_info *fs_info, * the async reclaim as we will panic. */ if (!test_bit(BTRFS_FS_LOG_RECOVERING, &fs_info->flags) && - need_preemptive_reclaim(fs_info, space_info, used) && + need_preemptive_reclaim(fs_info, space_info) && !work_busy(&fs_info->preempt_reclaim_work)) { trace_btrfs_trigger_flush(fs_info, space_info->flags, orig_bytes, flush, "preempt"); -- cgit v1.2.3