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author | David Rientjes <rientjes@google.com> | 2018-08-17 15:49:58 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2018-08-17 16:20:32 -0700 |
commit | ddbf369c0a33924f76d092985bd20d9310f43d7f (patch) | |
tree | cd24a886c4e71a26ad3f51e830a5e33e1b488b32 | |
parent | 6b51e88199ca4f75ff647eff28efd30bfcb08dc4 (diff) | |
download | op-kernel-dev-ddbf369c0a33924f76d092985bd20d9310f43d7f.zip op-kernel-dev-ddbf369c0a33924f76d092985bd20d9310f43d7f.tar.gz |
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>
-rw-r--r-- | include/linux/vmacache.h | 6 | ||||
-rw-r--r-- | mm/vmacache.c | 38 |
2 files changed, 29 insertions, 15 deletions
diff --git a/include/linux/vmacache.h b/include/linux/vmacache.h index a5b3aa8..3e9a963 100644 --- a/include/linux/vmacache.h +++ b/include/linux/vmacache.h @@ -5,12 +5,6 @@ #include <linux/sched.h> #include <linux/mm.h> -/* - * Hash based on the page number. Provides a good hit rate for - * workloads with good locality and those with random accesses as well. - */ -#define VMACACHE_HASH(addr) ((addr >> PAGE_SHIFT) & VMACACHE_MASK) - static inline void vmacache_flush(struct task_struct *tsk) { memset(tsk->vmacache.vmas, 0, sizeof(tsk->vmacache.vmas)); diff --git a/mm/vmacache.c b/mm/vmacache.c index db7596e..ea517be 100644 --- a/mm/vmacache.c +++ b/mm/vmacache.c @@ -6,6 +6,18 @@ #include <linux/sched/task.h> #include <linux/mm.h> #include <linux/vmacache.h> +#include <asm/pgtable.h> + +/* + * Hash based on the pmd of addr if configured with MMU, which provides a good + * hit rate for workloads with spatial locality. Otherwise, use pages. + */ +#ifdef CONFIG_MMU +#define VMACACHE_SHIFT PMD_SHIFT +#else +#define VMACACHE_SHIFT PAGE_SHIFT +#endif +#define VMACACHE_HASH(addr) ((addr >> VMACACHE_SHIFT) & VMACACHE_MASK) /* * Flush vma caches for threads that share a given mm. @@ -87,6 +99,7 @@ static bool vmacache_valid(struct mm_struct *mm) struct vm_area_struct *vmacache_find(struct mm_struct *mm, unsigned long addr) { + int idx = VMACACHE_HASH(addr); int i; count_vm_vmacache_event(VMACACHE_FIND_CALLS); @@ -95,16 +108,20 @@ struct vm_area_struct *vmacache_find(struct mm_struct *mm, unsigned long addr) return NULL; for (i = 0; i < VMACACHE_SIZE; i++) { - struct vm_area_struct *vma = current->vmacache.vmas[i]; + struct vm_area_struct *vma = current->vmacache.vmas[idx]; - if (!vma) - continue; - if (WARN_ON_ONCE(vma->vm_mm != mm)) - break; - if (vma->vm_start <= addr && vma->vm_end > addr) { - count_vm_vmacache_event(VMACACHE_FIND_HITS); - return vma; + if (vma) { +#ifdef CONFIG_DEBUG_VM_VMACACHE + if (WARN_ON_ONCE(vma->vm_mm != mm)) + break; +#endif + if (vma->vm_start <= addr && vma->vm_end > addr) { + count_vm_vmacache_event(VMACACHE_FIND_HITS); + return vma; + } } + if (++idx == VMACACHE_SIZE) + idx = 0; } return NULL; @@ -115,6 +132,7 @@ struct vm_area_struct *vmacache_find_exact(struct mm_struct *mm, unsigned long start, unsigned long end) { + int idx = VMACACHE_HASH(start); int i; count_vm_vmacache_event(VMACACHE_FIND_CALLS); @@ -123,12 +141,14 @@ struct vm_area_struct *vmacache_find_exact(struct mm_struct *mm, return NULL; for (i = 0; i < VMACACHE_SIZE; i++) { - struct vm_area_struct *vma = current->vmacache.vmas[i]; + struct vm_area_struct *vma = current->vmacache.vmas[idx]; if (vma && vma->vm_start == start && vma->vm_end == end) { count_vm_vmacache_event(VMACACHE_FIND_HITS); return vma; } + if (++idx == VMACACHE_SIZE) + idx = 0; } return NULL; |