[PATCH v7 1/2] malloc: add tcache support for large chunk caching

[Cupertino Miranda]

Hi Wilco,

Just seen this request.
What would you say to fix this with ?

diff --git a/malloc/malloc.c b/malloc/malloc.c
index 4cd0f728d2..5c51769ffd 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -3287,7 +3287,7 @@ tcache_index (size_t bytes)
        if (__glibc_likely (tc_idx < mp_.tcache_bins))
         return tc_idx;
      }
-  else
+  else if (bytes < mp_.tcache_max_bytes)
      {
        tc_idx = large_csize2tidx (bytes);
        if (tc_idx < mp_.tcache_bins)

The function large_csize2tidx is only called by tcache_index.
There is also another detail, that the value in mp_.tcache_max_bytes 
needs to become the chunk size and not allocation size.
mp_.tcache_max_bytes is not used anywhere else, either.

Cheers,
Cupertino

On 28-05-2025 00:27, Wilco Dijkstra wrote:
> Hi Cupertino,
> 
> Another thing, 64-bit targets may malloc over 4GB, so this will fail:
> 
>>> +              - __builtin_clz (nb);
> 
> You need to ensure it works for 32-bit and 64-bit size_t - clzl won't work
> since unsigned long is not always the same size as size_t, and while clzll
> should work, it has to be efficient on 32-bit targets (ie. not becoming a
> call when clz isn't a call). The new stdbit.h is type generic, so could be
> used, but we need to confirm that it results in good code.
> 
> Cheers,
> Wilco