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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 /include
parent6b51e88199ca4f75ff647eff28efd30bfcb08dc4 (diff)
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 'include')
-rw-r--r--include/linux/vmacache.h6
1 files changed, 0 insertions, 6 deletions
diff --git a/include/linux/vmacache.h b/include/linux/vmacache.h
index a5b3aa8d281f..3e9a963edd6a 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));