Re: [PATCH] cat: avoid memory allocation per file

[Pádraig Brady]

On 08/04/2026 15:11, Pádraig Brady wrote:

* src/cat.c (main): Only resize the allocated buffer when needed,
which avoids per file heap manipulation and mmap/munmap syscalls.
---

+static char *
+ensure_buf_size (char *buf, idx_t *buf_alloc, idx_t alignment, idx_t size)
+{
+  if (*buf_alloc < size)
+    {
+      alignfree (buf);
+      buf = xalignalloc (alignment, size);
+      *buf_alloc = size;
+    }
+
+  return buf;
+}
+

BTW I was tempted to avoid the valgrind / ASAN complaints
re using align_alloc() with non page aligned size, with the following,
but refrained since this was already considered as OK
as per the references in lib/alignalloc.h.
Hmm, maybe it's worth putting something like that in #ifdef lint.

diff --git a/src/cat.c b/src/cat.c
index 01a703e9b..04dd98a56 100644
--- a/src/cat.c
+++ b/src/cat.c
@@ -648,11 +648,17 @@ splice_cat (void)
 static char *
 ensure_buf_size (char *buf, idx_t *buf_alloc, idx_t alignment, idx_t size)
 {
-  if (*buf_alloc < size)
+  idx_t alloc_size = size;
+  idx_t remainder = size % alignment;
+  if (remainder
+      && ckd_add (&alloc_size, size, alignment - remainder))
+    xalloc_die ();
+
+  if (*buf_alloc < alloc_size)
     {
       alignfree (buf);
-      buf = xalignalloc (alignment, size);
-      *buf_alloc = size;
+      buf = xalignalloc (alignment, alloc_size);
+      *buf_alloc = alloc_size;
     }

   return buf;