Messages in this thread | | | Date | Mon, 22 Nov 2021 10:22:28 +0100 (CET) | From | Christoph Lameter <> | Subject | Re: [PATCH v4] slob: add size header to all allocations |
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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.
> @@ -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.
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