Re: [PATCH v4 3/3] selinux: use arrays for avtab hashtable nodes

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On Thu, Nov 2, 2023 at 11:45 AM Jacob Satterfield
<jsatterfield.linux@xxxxxxxxx> wrote:
>
> The current avtab hashtable employs a separate chaining collision
> resolution strategy where each bucket/chain holds an ordered linked list
> of pointers to kmem_cache allocated avtab_node elements.
>
> On Fedora 38 (x86_64) using the default policy, avtab_node_cachep
> uses 573 slabs each containing 170 objects totaling 2,337,840 bytes.
> A call to kmem_cache_zalloc() is required for every single rule, which
> in the default policy is currently 96,730 and continually rising.
>
> When both sets of avtab_node (regular and cond.) are turned into arrays
> with the hash table chain heads pointing into it, this results in only
> two additional kvcalloc() calls and the complete removal of the
> kmem_cache itself and its memory and runtime overheads.
>
> Running "perf stat -r 100 -d load_policy" has shown a runtime reduction
> of around 10% on a Fedora 38 x86_64 VM with this single patch. Future
> patches focused on improving the hash table's collision resolution
> strategy and array layout (struct-of-arrays vs. array-of-structs) may
> elicit even more caching and therefore runtime performance improvements.
>
> To prevent the conditional table from under-allocating the avtab_node
> array, which creates a heap-overflow bug, the two-pass algorithm in the
> patch "selinux: fix conditional avtab slot hint" is required.
>
> Signed-off-by: Jacob Satterfield <jsatterfield.linux@xxxxxxxxx>
> ---

This patch doesn't apply cleanly via git am; it will apply manually
with fuzz via patch but that suggests you sent the wrong version of
the patch rather than one based on the latest series.




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