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Subject[PATCH NG] alloc_pages_limit & pages_min
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Hi,

[Same patch as earlier sent to linux-mm, now tested]

Patch is agains 2.4.8-pre3, but should apply cleanly.
The only performance difference I have noticed is for copying
a huge file, then it performs a lot better (but I do not have a
baseline run for an unpatched -pre3, but I have benchmarked
both earlier and later revisions)

* The original code in __alloc_pages_limit has a little bug in
the case when:
- kreclaimd were not allowed to run for a LONG time...
Lots of kernel activity, RT tasks, or code running
around for a long time allocating memory.
- there were lots of inactive clean pages
- pages were allocated without direct_reclaim (higher order)
(networking might be one candidate)
it could result in using up ALL free pages!

This patch tries to prevent this situation in several ways:
1) Do not allow to alloc a free page when they are critically low.
[last line of patch, the really critical part of this patch]

2) If direct reclaims are allowed do some additional work.
reclaim & free until pages_min,
alloc one page,
reclaim and free until pages_low

/RogerL

--
Roger Larsson
Skellefteå
Sweden


*******************************************
Patch prepared by: roger.larsson@norran.net with comments from Riel

--- linux/mm/page_alloc.c.orig Wed Aug 22 13:36:57 2001
+++ linux/mm/page_alloc.c Thu Aug 23 01:15:17 2001
@@ -253,11 +253,35 @@

if (z->free_pages + z->inactive_clean_pages >= water_mark) {
struct page *page = NULL;
- /* If possible, reclaim a page directly. */
- if (direct_reclaim)
+
+ /*
+ * Reclaim a page from the inactive_clean list.
+ * If needed, refill the free list up to the
+ * low water mark.
+ */
+ if (direct_reclaim) {
page = reclaim_page(z);
- /* If that fails, fall back to rmqueue. */
- if (!page)
+
+ while (page && z->free_pages < z->pages_min) {
+ __free_page(page);
+ page = reclaim_page(z);
+ }
+
+ if (page) {
+ while (z->free_pages < z->pages_low) {
+ struct page *extra = reclaim_page(z);
+ if (!extra)
+ break;
+ __free_page(extra);
+ }
+ }
+
+ /* let kreclaimd handle up to pages_high */
+ }
+ /* If that fails, fall back to rmqueue, but never let
+ * free_pages go below pages_min...
+ */
+ if (!page && z->free_pages >= z->pages_min)
page = rmqueue(z, order);
if (page)
return page;
-
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