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bufbackoff() & freed pages
On 02/11/24(Sat) 13:01, Martin Pieuchot wrote:
> On 20/10/24(Sun) 11:33, Martin Pieuchot wrote:
> > This changes bufbackoff() to return the amount of recovered pages.
> > I'll be using this soon to access `uvmexp.free' only once per
> > iteration.
>
> I got a positive review. Any ok?
New version with some tweaks from tb@. ok?
Index: kern/vfs_bio.c
===================================================================
RCS file: /cvs/src/sys/kern/vfs_bio.c,v
diff -u -p -r1.213 vfs_bio.c
--- kern/vfs_bio.c 3 Feb 2024 18:51:58 -0000 1.213
+++ kern/vfs_bio.c 5 Nov 2024 16:16:57 -0000
@@ -284,22 +284,16 @@ bufadjust(int newbufpages)
}
/*
- * Make the buffer cache back off from cachepct.
+ * Back off "size" buffer cache pages. Called by the page
+ * daemon to consume buffer cache pages rather than scanning.
+ *
+ * It returns the number of freed pages.
*/
-int
+unsigned long
bufbackoff(struct uvm_constraint_range *range, long size)
{
- /*
- * Back off "size" buffer cache pages. Called by the page
- * daemon to consume buffer cache pages rather than scanning.
- *
- * It returns 0 to the pagedaemon to indicate that it has
- * succeeded in freeing enough pages. It returns -1 to
- * indicate that it could not and the pagedaemon should take
- * other measures.
- *
- */
long pdelta, oldbufpages;
+ int64_t dmarecovered, recovered = 0;
/*
* If we will accept high memory for this backoff
@@ -307,11 +301,13 @@ bufbackoff(struct uvm_constraint_range *
*/
if (range != NULL && range->ucr_high > dma_constraint.ucr_high) {
struct buf *bp;
- int64_t start = bcstats.numbufpages, recovered = 0;
- int s = splbio();
+ int64_t start;
+ int s;
- while ((recovered < size) &&
- (bp = bufcache_gethighcleanbuf())) {
+ start = bcstats.numbufpages;
+
+ s = splbio();
+ while (recovered < size && (bp = bufcache_gethighcleanbuf())) {
bufcache_take(bp);
if (bp->b_vp) {
RBT_REMOVE(buf_rb_bufs,
@@ -324,16 +320,13 @@ bufbackoff(struct uvm_constraint_range *
bufcache_adjust();
splx(s);
- /* If we got enough, return success */
+ /* We got enough. */
if (recovered >= size)
- return 0;
+ return recovered;
- /*
- * If we needed only memory above DMA,
- * return failure
- */
+ /* If we needed only memory above DMA, we're done. */
if (range->ucr_low > dma_constraint.ucr_high)
- return -1;
+ return recovered;
/* Otherwise get the rest from DMA */
size -= recovered;
@@ -351,15 +344,14 @@ bufbackoff(struct uvm_constraint_range *
pdelta = (size > bufbackpages) ? size : bufbackpages;
if (bufpages <= buflowpages)
- return(-1);
+ return recovered;
if (bufpages - pdelta < buflowpages)
pdelta = bufpages - buflowpages;
oldbufpages = bufpages;
bufadjust(bufpages - pdelta);
- if (oldbufpages - bufpages < size)
- return (-1); /* we did not free what we were asked */
- else
- return(0);
+ dmarecovered = oldbufpages - bufpages;
+
+ return recovered + dmarecovered;
}
Index: kern/vfs_biomem.c
===================================================================
RCS file: /cvs/src/sys/kern/vfs_biomem.c,v
diff -u -p -r1.51 vfs_biomem.c
--- kern/vfs_biomem.c 24 Oct 2021 00:02:25 -0000 1.51
+++ kern/vfs_biomem.c 5 Nov 2024 16:16:57 -0000
@@ -272,7 +272,7 @@ buf_alloc_pages(struct buf *bp, vsize_t
UVM_PLA_NOWAIT | UVM_PLA_NOWAKE);
if (i == 0)
break;
- } while (bufbackoff(&dma_constraint, size) == 0);
+ } while (bufbackoff(&dma_constraint, size) >= size);
if (i != 0)
i = uvm_pagealloc_multi(&bp->b_uobj, 0, size,
UVM_PLA_WAITOK);
@@ -324,6 +324,7 @@ int
buf_realloc_pages(struct buf *bp, struct uvm_constraint_range *where,
int flags)
{
+ vsize_t size;
vaddr_t va;
int dma;
int i, r;
@@ -345,7 +346,8 @@ buf_realloc_pages(struct buf *bp, struct
bp->b_bufsize, UVM_PLA_NOWAIT | UVM_PLA_NOWAKE, where);
if (r == 0)
break;
- } while ((bufbackoff(where, atop(bp->b_bufsize)) == 0));
+ size = atop(bp->b_bufsize);
+ } while ((bufbackoff(where, size) >= size));
/*
* bufbackoff() failed, so there's no more we can do without
Index: uvm/uvm_pdaemon.c
===================================================================
RCS file: /cvs/src/sys/uvm/uvm_pdaemon.c,v
diff -u -p -r1.120 uvm_pdaemon.c
--- uvm/uvm_pdaemon.c 5 Nov 2024 15:29:00 -0000 1.120
+++ uvm/uvm_pdaemon.c 5 Nov 2024 16:16:57 -0000
@@ -132,7 +132,7 @@ uvm_wait(const char *wmsg)
*/
if (curproc == uvm.pagedaemon_proc) {
printf("uvm_wait emergency bufbackoff\n");
- if (bufbackoff(NULL, 4) == 0)
+ if (bufbackoff(NULL, 4) >= 4)
return;
/*
* now we have a problem: the pagedaemon wants to go to
Index: uvm/uvm_pmemrange.c
===================================================================
RCS file: /cvs/src/sys/uvm/uvm_pmemrange.c,v
diff -u -p -r1.68 uvm_pmemrange.c
--- uvm/uvm_pmemrange.c 2 Oct 2024 10:17:28 -0000 1.68
+++ uvm/uvm_pmemrange.c 5 Nov 2024 16:16:57 -0000
@@ -2104,7 +2104,7 @@ uvm_wait_pla(paddr_t low, paddr_t high, *
easily use up that reserve in a single scan iteration.
*/
uvm_unlock_fpageq();
- if (bufbackoff(NULL, atop(size)) == 0) {
+ if (bufbackoff(NULL, atop(size)) >= atop(size)) {
uvm_lock_fpageq();
return 0;
}
Index: sys/mount.h
===================================================================
RCS file: /cvs/src/sys/sys/mount.h,v
diff -u -p -r1.151 mount.h
--- sys/mount.h 3 Feb 2024 18:51:58 -0000 1.151
+++ sys/mount.h 5 Nov 2024 16:16:57 -0000
@@ -495,7 +495,7 @@ extern long buflowpages, bufhighpages, b
extern int bufcachepercent;
extern void bufadjust(int);
struct uvm_constraint_range;
-extern int bufbackoff(struct uvm_constraint_range*, long);
+extern unsigned long bufbackoff(struct uvm_constraint_range*, long);
/*
* Operations supported on mounted file system.
bufbackoff() & freed pages