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adjust heuristics for read-ahead to skip the full read-ahead when last page of

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the range is already cached; this speeds up I/O from cache, since it avoids
the lookup and allocation overhead

on my system I observed 4.5% - 15% improvement for cached I/O - from 2.2 GB/s to
2.3 GB/s for cached reads using non-direct UBC, and from 5.6 GB/s to 6.5 GB/s
for UBC using direct map

part of PR kern/53124
This commit is contained in:
jdolecek 2018-05-19 15:18:02 +00:00
parent 6a369df7db
commit 9b785b5267
1 changed files with 20 additions and 3 deletions
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23
sys/uvm/uvm_readahead.c
View File

@ -1,4 +1,4 @@
/* $NetBSD: uvm_readahead.c,v 1.9 2018/03/30 07:22:59 mlelstv Exp $ */
/* $NetBSD: uvm_readahead.c,v 1.10 2018/05/19 15:18:02 jdolecek Exp $ */
/*-
* Copyright (c)2003, 2005, 2009 YAMAMOTO Takashi,
@ -40,7 +40,7 @@
*/
#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: uvm_readahead.c,v 1.9 2018/03/30 07:22:59 mlelstv Exp $");
__KERNEL_RCSID(0, "$NetBSD: uvm_readahead.c,v 1.10 2018/05/19 15:18:02 jdolecek Exp $");
#include <sys/param.h>
#include <sys/pool.h>
@ -125,6 +125,23 @@ ra_startio(struct uvm_object *uobj, off_t off, size_t sz)
DPRINTF(("%s: uobj=%p, off=%" PRIu64 ", endoff=%" PRIu64 "\n",
__func__, uobj, off, endoff));
/*
* Don't issue read-ahead if the last page of the range is already cached.
* The assumption is that since the access is sequential, the intermediate
* pages would have similar LRU stats, and hence likely to be still in cache
* too. This speeds up I/O using cache, since it avoids lookups and temporary
* allocations done by full pgo_get.
*/
mutex_enter(uobj->vmobjlock);
struct vm_page *pg = uvm_pagelookup(uobj, trunc_page(endoff - 1));
mutex_exit(uobj->vmobjlock);
if (pg != NULL) {
DPRINTF(("%s: off=%" PRIu64 ", sz=%zu already cached\n",
__func__, off, sz));
return endoff;
}
off = trunc_page(off);
while (off < endoff) {
const size_t chunksize = RA_IOCHUNK;
@ -147,7 +164,7 @@ ra_startio(struct uvm_object *uobj, off_t off, size_t sz)
mutex_enter(uobj->vmobjlock);
error = (*uobj->pgops->pgo_get)(uobj, off, NULL,
&npages, 0, VM_PROT_READ, UVM_ADV_RANDOM, 0);
&npages, 0, VM_PROT_READ, UVM_ADV_RANDOM, PGO_NOTIMESTAMP);
DPRINTF(("%s: off=%" PRIu64 ", bytelen=%zu -> %d\n",
__func__, off, bytelen, error));
if (error != 0 && error != EBUSY) {