On Thu, 27 Sep 2007 15:21:21 -0700
Andrew Morton <[email protected]> wrote:
> > Nope, sc.nr_io_pages will also be incremented when the code runs into
> > pages that are already PageWriteback.
>
> yup, I didn't think of that. Hopefully someone else will be in there
> working on that zone too. If this caller yields and defers to kswapd
> then that's very likely. Except we just took away the ability to do that..
if (PageDirty(page)) {
if (sc->order <= PAGE_ALLOC_COSTLY_ORDER && referenced)
goto keep_locked;
if (!may_enter_fs)
goto keep_locked;
I think we can fix that problem by adding a sc->nr_io_pages++
between the last if and the goto keep_locked in shrink_page_list.
That way !GFP_IO or !GFP_FS tasks will cause themselves to sleep
if there are pages that need to be written out, even if those
pages are not in flight to disk yet.
I have also added the comment you wanted.
Signed-off-by: Rik van Riel <[email protected]>
diff -up linux-2.6.23-rc7/mm/vmscan.c.wait linux-2.6.22/mm/vmscan.c
--- linux-2.6.23-rc7/mm/vmscan.c.wait 2007-09-27 18:45:57.000000000 -0400
+++ linux-2.6.23-rc7/mm/vmscan.c 2007-09-27 18:48:43.000000000 -0400
@@ -68,6 +68,13 @@ struct scan_control {
int all_unreclaimable;
int order;
+
+ /*
+ * Pages that have (or should have) IO pending. If we run into
+ * a lot of these, we're better off waiting a little for IO to
+ * finish rather than scanning more pages in the VM.
+ */
+ int nr_io_pages;
};
#define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
@@ -489,8 +496,10 @@ static unsigned long shrink_page_list(st
*/
if (sync_writeback == PAGEOUT_IO_SYNC && may_enter_fs)
wait_on_page_writeback(page);
- else
+ else {
+ sc->nr_io_pages++;
goto keep_locked;
+ }
}
referenced = page_referenced(page, 1);
@@ -529,8 +538,10 @@ static unsigned long shrink_page_list(st
if (PageDirty(page)) {
if (sc->order <= PAGE_ALLOC_COSTLY_ORDER && referenced)
goto keep_locked;
- if (!may_enter_fs)
+ if (!may_enter_fs) {
+ sc->nr_io_pages++;
goto keep_locked;
+ }
if (!sc->may_writepage)
goto keep_locked;
@@ -541,8 +552,10 @@ static unsigned long shrink_page_list(st
case PAGE_ACTIVATE:
goto activate_locked;
case PAGE_SUCCESS:
- if (PageWriteback(page) || PageDirty(page))
+ if (PageWriteback(page) || PageDirty(page)) {
+ sc->nr_io_pages++;
goto keep;
+ }
/*
* A synchronous write - probably a ramdisk. Go
* ahead and try to reclaim the page.
@@ -1201,6 +1214,7 @@ unsigned long try_to_free_pages(struct z
for (priority = DEF_PRIORITY; priority >= 0; priority--) {
sc.nr_scanned = 0;
+ sc.nr_io_pages = 0;
if (!priority)
disable_swap_token();
nr_reclaimed += shrink_zones(priority, zones, &sc);
@@ -1229,7 +1243,8 @@ unsigned long try_to_free_pages(struct z
}
/* Take a nap, wait for some writeback to complete */
- if (sc.nr_scanned && priority < DEF_PRIORITY - 2)
+ if (sc.nr_scanned && priority < DEF_PRIORITY - 2 &&
+ sc.nr_io_pages > sc.swap_cluster_max)
congestion_wait(WRITE, HZ/10);
}
/* top priority shrink_caches still had more to do? don't OOM, then */
@@ -1315,6 +1330,7 @@ loop_again:
if (!priority)
disable_swap_token();
+ sc.nr_io_pages = 0;
all_zones_ok = 1;
/*
@@ -1398,7 +1414,8 @@ loop_again:
* OK, kswapd is getting into trouble. Take a nap, then take
* another pass across the zones.
*/
- if (total_scanned && priority < DEF_PRIORITY - 2)
+ if (total_scanned && priority < DEF_PRIORITY - 2 &&
+ sc.nr_io_pages > sc.swap_cluster_max)
congestion_wait(WRITE, HZ/10);
/*
-
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