diff options
| author | David Rientjes <rientjes@google.com> | 2018-08-17 15:49:58 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2018-08-17 16:20:32 -0700 |
| commit | ddbf369c0a33924f76d092985bd20d9310f43d7f (patch) | |
| tree | cd24a886c4e71a26ad3f51e830a5e33e1b488b32 /include | |
| parent | 6b51e88199ca4f75ff647eff28efd30bfcb08dc4 (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.h | 6 |
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)); |