From: Alexey Dobriyan <adobriyan@xxxxxxxxx> Subject: mm: unrig VMA cache hit ratio Current code doesn't count first FIND operation after VMA cache flush (which happen surprisingly often) artificially increasing cache hit ratio. On my regular setup the difference is: Before After ========================================================== * boot, login into KDE vmacache_find_calls 446216 vmacache_find_calls 492741 vmacache_find_hits 277596 vmacache_find_hits 276096 ~62.2% ~56.0% * rebuild kernel (no changes to code, usual config) vmacache_find_calls 1943007 vmacache_find_calls 2083718 vmacache_find_hits 1246123 vmacache_find_hits 1244146 ~64.1% ~59.7% * rebuild kernel (full rebuild, usual config) vmacache_find_calls 32163155 vmacache_find_calls 33677183 vmacache_find_hits 27889956 vmacache_find_hits 27877591 ~88.2% ~84.3% Total: ~4% cache hit ratio. If someone is counting _relative_ cache _miss_ ratio, misreporting is much higher. Link: http://lkml.kernel.org/r/20160822225009.GA3934@xxxxxxxxxxxxxxx Signed-off-by: Alexey Dobriyan <adobriyan@xxxxxxxxx> Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/vmacache.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff -puN mm/vmacache.c~mm-unrig-vma-cache-hit-ratio mm/vmacache.c --- a/mm/vmacache.c~mm-unrig-vma-cache-hit-ratio +++ a/mm/vmacache.c @@ -87,11 +87,11 @@ struct vm_area_struct *vmacache_find(str { int i; + count_vm_vmacache_event(VMACACHE_FIND_CALLS); + if (!vmacache_valid(mm)) return NULL; - count_vm_vmacache_event(VMACACHE_FIND_CALLS); - for (i = 0; i < VMACACHE_SIZE; i++) { struct vm_area_struct *vma = current->vmacache[i]; @@ -115,11 +115,11 @@ struct vm_area_struct *vmacache_find_exa { int i; + count_vm_vmacache_event(VMACACHE_FIND_CALLS); + if (!vmacache_valid(mm)) return NULL; - count_vm_vmacache_event(VMACACHE_FIND_CALLS); - for (i = 0; i < VMACACHE_SIZE; i++) { struct vm_area_struct *vma = current->vmacache[i]; _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
