mirror of https://gitee.com/openkylin/linux.git
mm, vmacache: hash addresses based on pmd
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>
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@ -5,12 +5,6 @@
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#include <linux/sched.h>
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#include <linux/mm.h>
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/*
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* Hash based on the page number. Provides a good hit rate for
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* workloads with good locality and those with random accesses as well.
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*/
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#define VMACACHE_HASH(addr) ((addr >> PAGE_SHIFT) & VMACACHE_MASK)
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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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@ -6,6 +6,18 @@
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#include <linux/sched/task.h>
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#include <linux/mm.h>
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#include <linux/vmacache.h>
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#include <asm/pgtable.h>
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/*
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* Hash based on the pmd of addr if configured with MMU, which provides a good
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* hit rate for workloads with spatial locality. Otherwise, use pages.
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*/
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#ifdef CONFIG_MMU
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#define VMACACHE_SHIFT PMD_SHIFT
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#else
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#define VMACACHE_SHIFT PAGE_SHIFT
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#endif
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#define VMACACHE_HASH(addr) ((addr >> VMACACHE_SHIFT) & VMACACHE_MASK)
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/*
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* Flush vma caches for threads that share a given mm.
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@ -87,6 +99,7 @@ static bool vmacache_valid(struct mm_struct *mm)
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struct vm_area_struct *vmacache_find(struct mm_struct *mm, unsigned long addr)
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{
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int idx = VMACACHE_HASH(addr);
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int i;
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count_vm_vmacache_event(VMACACHE_FIND_CALLS);
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@ -95,16 +108,20 @@ struct vm_area_struct *vmacache_find(struct mm_struct *mm, unsigned long addr)
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return NULL;
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for (i = 0; i < VMACACHE_SIZE; i++) {
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struct vm_area_struct *vma = current->vmacache.vmas[i];
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struct vm_area_struct *vma = current->vmacache.vmas[idx];
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if (!vma)
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continue;
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if (WARN_ON_ONCE(vma->vm_mm != mm))
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break;
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if (vma->vm_start <= addr && vma->vm_end > addr) {
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count_vm_vmacache_event(VMACACHE_FIND_HITS);
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return vma;
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if (vma) {
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#ifdef CONFIG_DEBUG_VM_VMACACHE
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if (WARN_ON_ONCE(vma->vm_mm != mm))
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break;
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#endif
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if (vma->vm_start <= addr && vma->vm_end > addr) {
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count_vm_vmacache_event(VMACACHE_FIND_HITS);
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return vma;
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}
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}
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if (++idx == VMACACHE_SIZE)
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idx = 0;
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}
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return NULL;
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@ -115,6 +132,7 @@ 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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{
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int idx = VMACACHE_HASH(start);
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int i;
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count_vm_vmacache_event(VMACACHE_FIND_CALLS);
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@ -123,12 +141,14 @@ struct vm_area_struct *vmacache_find_exact(struct mm_struct *mm,
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return NULL;
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for (i = 0; i < VMACACHE_SIZE; i++) {
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struct vm_area_struct *vma = current->vmacache.vmas[i];
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struct vm_area_struct *vma = current->vmacache.vmas[idx];
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if (vma && vma->vm_start == start && vma->vm_end == end) {
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count_vm_vmacache_event(VMACACHE_FIND_HITS);
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return vma;
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}
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if (++idx == VMACACHE_SIZE)
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idx = 0;
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}
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return NULL;
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