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kernel: keep cached pages continuous at the end of the page list on imagereclaim()

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imagereclaim() sabotaged itself by breaking the invariant
that cached pages are kept at the end of the page list.

once we made a hole of uncached pages, we would stop
reclaiming cached pages before it as the loop breaks
once it hits a uncached page. (we iterate backwards from
the tail to the head of the pagelist until pages have been
reclaimed or we hit a uncached page).

the solution is to move pages to the head of the pagelist
after removing them from the image cache.
This commit is contained in:
cinap_lenrek 2014-02-24 22:42:22 +01:00
parent 60c3c3b3db
commit 521a34d33b
3 changed files with 9 additions and 3 deletions
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2
sys/src/9/port/page.c
View file

@ -64,7 +64,7 @@ pageinit(void)
print("%ldM swap\n", vkb/1024); print("%ldM swap\n", vkb/1024);
} }
static void void
pageunchain(Page *p) pageunchain(Page *p)
{ {
if(canlock(&palloc)) if(canlock(&palloc))

1
sys/src/9/port/portfns.h
View file

@ -202,6 +202,7 @@ int okaddr(uintptr, ulong, int);
int openmode(ulong); int openmode(ulong);
Block* packblock(Block*); Block* packblock(Block*);
Block* padblock(Block*, int); Block* padblock(Block*, int);
void pageunchain(Page*);
void pagechainhead(Page*); void pagechainhead(Page*);
void pageinit(void); void pageinit(void);
ulong pagenumber(Page*); ulong pagenumber(Page*);

9
sys/src/9/port/segment.c
View file

@ -313,7 +313,7 @@ static void
imagereclaim(void) imagereclaim(void)
{ {
int n; int n;
Page *p; Page *p, *x;
uvlong ticks; uvlong ticks;
irstats.calls++; irstats.calls++;
@ -329,11 +329,16 @@ imagereclaim(void)
* end of the list (see putpage) so start there and work * end of the list (see putpage) so start there and work
* backward. * backward.
*/ */
for(p = palloc.tail; p && p->image && (n<1000 || !imagealloc.free); p = p->prev) { for(p = palloc.tail; p && p->image && (n<1000 || !imagealloc.free); p = x) {
x = p->prev;
if(p->ref == 0 && canlock(p)) { if(p->ref == 0 && canlock(p)) {
if(p->ref == 0 && p->image && !p->image->notext) { if(p->ref == 0 && p->image && !p->image->notext) {
n++; n++;
uncachepage(p); uncachepage(p);
/* move to head to maintain the invariant above */
pageunchain(p);
pagechainhead(p);
} }
unlock(p); unlock(p);
} }