On Tue, 22 Oct 2013 14:53:59 +0300 "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> wrote:
> If DEBUG_SPINLOCK and DEBUG_LOCK_ALLOC are enabled spinlock_t on x86_64
> is 72 bytes. For page->ptl they will be allocated from kmalloc-96 slab,
> so we loose 24 on each. An average system can easily allocate few tens
> thousands of page->ptl and overhead is significant.
>
> Let's create a separate slab for page->ptl allocation to solve this.
>
> ...
>
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -4332,11 +4332,19 @@ void copy_user_huge_page(struct page *dst, struct page *src,
> #endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HUGETLBFS */
>
> #if USE_SPLIT_PTE_PTLOCKS
> +struct kmem_cache *page_ptl_cachep;
> +void __init ptlock_cache_init(void)
> +{
> + if (sizeof(spinlock_t) > sizeof(long))
> + page_ptl_cachep = kmem_cache_create("page->ptl",
> + sizeof(spinlock_t), 0, SLAB_PANIC, NULL);
> +}
Confused. If (sizeof(spinlock_t) > sizeof(long)) happens to be false
then the kernel will later crash. It would be better to use BUILD_BUG_ON()
here, if that works. Otherwise BUG_ON.
Also, we have the somewhat silly KMEM_CACHE() macro, but it looks
inapplicable here?
> bool __ptlock_alloc(struct page *page)
> {
> spinlock_t *ptl;
>
> - ptl = kmalloc(sizeof(spinlock_t), GFP_KERNEL);
> + ptl = kmem_cache_alloc(page_ptl_cachep, GFP_KERNEL);
> if (!ptl)
> return false;
> page->ptl = (unsigned long)ptl;
> @@ -4346,6 +4354,6 @@ bool __ptlock_alloc(struct page *page)
> void __ptlock_free(struct page *page)
> {
> if (sizeof(spinlock_t) > sizeof(page->ptl))
> - kfree((spinlock_t *)page->ptl);
> + kmem_cache_free(page_ptl_cachep, (spinlock_t *)page->ptl);
A void* cast would suffice here, but I suppose the spinlock_t* cast has
some documentation value.
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