Re: [PATCH v4] slob: add size header to all allocations
From: Christoph Lameter <cl@gentwo.org>
Date: 2021-11-22 09:28:55
Also in:
linux-mm, lkml
On Sun, 21 Nov 2021, Rustam Kovhaev wrote:
Let's prepend both kmalloc() and kmem_cache_alloc() allocations with the size header. It simplifies the slab API and guarantees that both kmem_cache_alloc() and kmalloc() memory could be freed by kfree(). meminfo right after the system boot, x86-64 on xfs, without the patch: Slab: 34700 kB the same, with the patch: Slab: 35752 kB
+#define SLOB_HDR_SIZE max(ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN)
Ok that is up to 128 bytes on some architectues. Mostly 32 or 64 bytes.
quoted hunk ↗ jump to hunk
@@ -307,6 +303,7 @@ static void *slob_alloc(size_t size, gfp_t gfp, int align, int node, unsigned long flags; bool _unused; + size += SLOB_HDR_SIZE;
And every object now has this overhead? 128 bytes extra in extreme cases per object?
- if (size < PAGE_SIZE - minalign) {
- int align = minalign;
+ if (size < PAGE_SIZE - SLOB_HDR_SIZE) {
+ int align = SLOB_HDR_SIZE;And the object is also aligned to 128 bytes boundaries on some architectures. So a 4 byte object occupies 256 bytes in SLOB? SLOB will no longer be a low memory overhead allocator then.