Re: [PATCH 2/3] maple_tree: use preallocations in mas_store_gfp()

From: Sidhartha Kumar
Date: Tue Oct 10 2023 - 20:17:43 EST


On 10/9/23 8:03 PM, Peng Zhang wrote:
Hi,

在 2023/10/10 04:16, Sidhartha Kumar 写道:
Preallocate maple nodes before call to mas_wr_store_entry(). If a new
node is not needed, go directly to mas_wr_store_entry(), otherwise
allocate the needed nodes and set the MA_STATE_PREALLOC flag.

Signed-off-by: Sidhartha Kumar <sidhartha.kumar@xxxxxxxxxx>
---
  lib/maple_tree.c | 22 +++++++++++++++++++---
  1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index e239197a57fc..25ae66e585f4 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -5478,17 +5478,33 @@ int mas_prealloc_calc(struct ma_wr_state *wr_mas)
  int mas_store_gfp(struct ma_state *mas, void *entry, gfp_t gfp)
  {
      MA_WR_STATE(wr_mas, mas, entry);
+    int request;
      mas_wr_store_setup(&wr_mas);
-    trace_ma_write(__func__, mas, 0, entry);
-retry:
+    wr_mas.content = mas_start(mas);
+
+    request = mas_prealloc_calc(&wr_mas);
mas_wr_store_entry() does something similar to mas_prealloc_calc().
Now, making it do it twice would incur additional overhead.
We encountered this issue while optimizing preallocation, but it
hasn't been resolved yet. Previously, this problem only occurred
when using mas_preallocate(). Now, this change would bring this
impact to all write operations on maple tree. What do you think
about it?


After talking to Liam, I will have to implement the store type enum feature on the Maple Tree Work list so that mas_prealloc_calc() can start a partial walk and write that information to the enum. mas_wr_store_entry() can then read that enum to continue the walk that was already started rather than having to redo the whole walk. This could also be used in mas_preallocate(). Do you have any suggestions for the implementation of this enum?

Thanks,
Sid

Thanks,
Peng
+    if (!request)
+        goto store_entry;
+
+    mas_node_count_gfp(mas, request, gfp);
+    if (unlikely(mas_is_err(mas))) {
+        mas_set_alloc_req(mas, 0);
+        mas_destroy(mas);
+        mas_reset(mas);
+        return xa_err(mas->node);
+    }
+    mas->mas_flags |= MA_STATE_PREALLOC;
+
+store_entry:
      mas_wr_store_entry(&wr_mas);
      if (unlikely(mas_nomem(mas, gfp)))
-        goto retry;
+        goto store_entry;
      if (unlikely(mas_is_err(mas)))
          return xa_err(mas->node);
+    trace_ma_write(__func__, mas, 0, entry);
      return 0;
  }
  EXPORT_SYMBOL_GPL(mas_store_gfp);