Messages in this thread Patch in this message |  | | Date | Tue, 17 Sep 2002 23:48:04 +0200 | From | "Juan M. de la Torre" <> | Subject | Possible bug in __alloc_pages() ? |
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Hi, this code appears at the beggining of __page_alloc() (kernel 2.4.19):
min = 1UL << order; for (;;) { zone_t *z = *(zone++); if (!z) break;
min += z->pages_low; if (z->free_pages > min) { page = rmqueue(z, order); if (page) return page; } }
AFAIK, what this code does is to try to alloc the requested pages from the first zone in a zone_list (passed as argument) which have enought free pages.
A zone is considered to have enought free pages if z->free_pages is greater than (number_of_requested_pages + z->pages_low).
In the loop shown, the first iteration is OK, but in the second iteration (which only occurs if the first zone in the zone_list hasn't enought free pages) the zone will only be considered to have enought free pages if z->free_pages is greater that (number_of_requested_pages + z->pages_low + PREV_ZONE->pages_low).
I think this is a bug, but i'm not sure (i'm not a VM hacker).
If it is a bug, there are other two loops in the same function which are buggy.
Possible patch:
--- linux/mm/page_alloc.c.orig Tue Sep 17 23:45:02 2002 +++ linux/mm/page_alloc.c Tue Sep 17 23:46:45 2002 @@ -330,8 +330,7 @@ if (!z) break;
- min += z->pages_low; - if (z->free_pages > min) { + if (z->free_pages > min + z->pages_low) { page = rmqueue(z, order); if (page) return page; @@ -354,8 +353,8 @@ local_min = z->pages_min; if (!(gfp_mask & __GFP_WAIT)) local_min >>= 2; - min += local_min; - if (z->free_pages > min) { + + if (z->free_pages > min + local_min) { page = rmqueue(z, order); if (page) return page; @@ -394,8 +393,7 @@ if (!z) break;
- min += z->pages_min; - if (z->free_pages > min) { + if (z->free_pages > min + z->pages_min) { page = rmqueue(z, order); if (page) return page; Regards, Juanma
-- /jm
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