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authorDavid Rientjes <rientjes@google.com>2018-08-17 15:49:58 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2018-08-17 16:20:32 -0700
commitddbf369c0a33924f76d092985bd20d9310f43d7f (patch)
treecd24a886c4e71a26ad3f51e830a5e33e1b488b32 /mm
parent6b51e88199ca4f75ff647eff28efd30bfcb08dc4 (diff)
downloadlinux-stericsson-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>
Diffstat (limited to 'mm')
-rw-r--r--mm/vmacache.c38
1 files changed, 29 insertions, 9 deletions
diff --git a/mm/vmacache.c b/mm/vmacache.c
index db7596eb6132..ea517bef7dc5 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;