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Fix a performance problem with the new getnewbuf() code: in an outofspace

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condition ( bufspace > hibufspace ), an inappropriate scan of the empty
queue was performed looking for buffer space to free up.

Submitted by:	Matthew Dillon <dillon@apollo.backplane.com>
This commit is contained in:
Alan Cox 1999-04-07 02:41:54 +00:00
parent 143b4dcdc7
commit b2e2337ba1
1 changed files with 31 additions and 27 deletions
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58
sys/kern/vfs_bio.c
View File

@ -11,7 +11,7 @@
* 2. Absolutely no warranty of function or purpose is made by the author
* John S. Dyson.
*
* $Id: vfs_bio.c,v 1.203 1999/03/19 10:17:44 bde Exp $
* $Id: vfs_bio.c,v 1.204 1999/04/05 19:38:30 julian Exp $
*/
/*
@ -1132,32 +1132,6 @@ getnewbuf(struct vnode *vp, daddr_t blkno,
int countawrites = 0;
restart:
/*
* Setup for scan. If we do not have enough free buffers,
* we setup a degenerate case that falls through the while.
*
* If we are in the middle of a flush, we can dip into the
* emergency reserve.
*/
if ((curproc->p_flag & P_FLSINPROG) == 0 &&
numfreebuffers < lofreebuffers
) {
nqindex = QUEUE_LRU;
nbp = NULL;
} else {
nqindex = QUEUE_EMPTY;
if ((nbp = TAILQ_FIRST(&bufqueues[QUEUE_EMPTY])) == NULL) {
nqindex = QUEUE_AGE;
nbp = TAILQ_FIRST(&bufqueues[QUEUE_AGE]);
if (nbp == NULL) {
nqindex = QUEUE_LRU;
nbp = TAILQ_FIRST(&bufqueues[QUEUE_LRU]);
}
}
}
/*
* Calculate whether we are out of buffer space. This state is
* recalculated on every restart. If we are out of space, we
@ -1182,6 +1156,36 @@ restart:
*/
/* nop */
/*
* Setup for scan. If we do not have enough free buffers,
* we setup a degenerate case that falls through the while.
*
* If we are in the middle of a flush, we can dip into the
* emergency reserve.
*
* If we are out of space, we skip trying to scan QUEUE_EMPTY
* because those buffers are, well, empty.
*/
if ((curproc->p_flag & P_FLSINPROG) == 0 &&
numfreebuffers < lofreebuffers
) {
nqindex = QUEUE_LRU;
nbp = NULL;
} else {
nqindex = QUEUE_EMPTY;
if (outofspace ||
(nbp = TAILQ_FIRST(&bufqueues[QUEUE_EMPTY])) == NULL
) {
nqindex = QUEUE_AGE;
nbp = TAILQ_FIRST(&bufqueues[QUEUE_AGE]);
if (nbp == NULL) {
nqindex = QUEUE_LRU;
nbp = TAILQ_FIRST(&bufqueues[QUEUE_LRU]);
}
}
}
/*
* Run scan, possibly freeing data and/or kva mappings on the fly
* depending.