Re: [PATCH] btrfs: Optimise space flushing machinery

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On 3/11/20 1:57 PM, Nikolay Borisov wrote:


On 11.03.20 г. 19:52 ч., Josef Bacik wrote:
On 3/10/20 5:00 AM, Nikolay Borisov wrote:
Instead of iterating all pending tickets on the normal/priority list to
sum their total size the cost can be amortized across ticket addition/
removal. This turns O(n) + O(m) (where n is the size of the normal list
and m of the priority list) into O(1). This will mostly have effect in
workloads
that experience heavy flushing.

Signed-off-by: Nikolay Borisov <nborisov@xxxxxxxx>
---
   fs/btrfs/space-info.c | 13 ++++++++-----
   fs/btrfs/space-info.h |  4 ++++
   2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/fs/btrfs/space-info.c b/fs/btrfs/space-info.c
index 9cb511d8cd9d..316a724dc990 100644
--- a/fs/btrfs/space-info.c
+++ b/fs/btrfs/space-info.c
@@ -389,6 +389,8 @@ void btrfs_try_granting_tickets(struct
btrfs_fs_info *fs_info,
                                     space_info,
                                     ticket->bytes);
               list_del_init(&ticket->list);
+            ASSERT(space_info->reclaim_size >= ticket->bytes);
+            space_info->reclaim_size -= ticket->bytes;
               ticket->bytes = 0;
               space_info->tickets_id++;
               wake_up(&ticket->wait);
@@ -784,16 +786,15 @@ static inline u64
   btrfs_calc_reclaim_metadata_size(struct btrfs_fs_info *fs_info,
                    struct btrfs_space_info *space_info)
   {
-    struct reserve_ticket *ticket;
       u64 used;
       u64 avail;
       u64 expected;
       u64 to_reclaim = 0;

-    list_for_each_entry(ticket, &space_info->tickets, list)
-        to_reclaim += ticket->bytes;
-    list_for_each_entry(ticket, &space_info->priority_tickets, list)
-        to_reclaim += ticket->bytes;
+    lockdep_assert_held(&space_info->lock);
+
+    if (space_info->reclaim_size)
+        return space_info->reclaim_size;

This undoes the fix that I put up making sure we include any space we
can no longer overcommit.  Thanks,

Which fix is that?

https://github.com/kdave/btrfs-devel/commit/593212a6137ff3c5674609b4233f8ecec459dc45

Thanks,

Josef



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