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When perf profiling a wide variety of different workloads, it was found that vmacache_find() had higher than expected cost: up to 0.08% of cpu utilization in some cases. This was found to rival other core VM functions such as alloc_pages_vma() with thp enabled and default mempolicy, and the conditionals in __get_vma_policy(). VMACACHE_HASH() determines which of the four per-task_struct slots a vma is cached for a particular address. This currently depends on the pfn, so pfn 5212 occupies a different vmacache slot than its neighboring pfn 5213. vmacache_find() iterates through all four of current's vmacache slots when looking up an address. Hashing based on pfn, an address has ~1/VMACACHE_SIZE chance of being cached in the first vmacache slot, or about 25%, *if* the vma is cached. This patch hashes an address by its pmd instead of pte to optimize for workloads with good spatial locality. This results in a higher probability of vmas being cached in the first slot that is checked: normally ~70% on the same workloads instead of 25%. [rientjes@google.com: various updates] Link: http://lkml.kernel.org/r/alpine.DEB.2.21.1807231532290.109445@chino.kir.corp.google.com Link: http://lkml.kernel.org/r/alpine.DEB.2.21.1807091749150.114630@chino.kir.corp.google.com Signed-off-by: David Rientjes <rientjes@google.com> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Alexey Dobriyan <adobriyan@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
33 lines
871 B
C
33 lines
871 B
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef __LINUX_VMACACHE_H
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#define __LINUX_VMACACHE_H
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#include <linux/sched.h>
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#include <linux/mm.h>
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static inline void vmacache_flush(struct task_struct *tsk)
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{
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memset(tsk->vmacache.vmas, 0, sizeof(tsk->vmacache.vmas));
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}
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extern void vmacache_flush_all(struct mm_struct *mm);
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extern void vmacache_update(unsigned long addr, struct vm_area_struct *newvma);
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extern struct vm_area_struct *vmacache_find(struct mm_struct *mm,
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unsigned long addr);
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#ifndef CONFIG_MMU
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extern struct vm_area_struct *vmacache_find_exact(struct mm_struct *mm,
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unsigned long start,
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unsigned long end);
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#endif
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static inline void vmacache_invalidate(struct mm_struct *mm)
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{
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mm->vmacache_seqnum++;
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/* deal with overflows */
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if (unlikely(mm->vmacache_seqnum == 0))
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vmacache_flush_all(mm);
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}
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#endif /* __LINUX_VMACACHE_H */
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