High order memory allocations (was Re: Memory Problem in

[Alex Bligh - linux-kernel]

Next problem / idea:

memory_pressure sets the target for inactive_target (hence
free_target etc.)

However, if you do (say) and order 5 allocation, memory
pressure is only incremented by 1. This seems illogical,
especially given __alloc_pages does not loop via
try_again, on order>0 allocations (except
when freeshortage() is true) even if __GFP_WAIT
is set (I suspect because it just sits there for
ever). In practice, this means page_launder only
has one shot at freeing sufficient pages, and this
with a wrong inactive target. I propose something
like (whitespace broken - sorry):

--- mm/page_alloc.c.keep   Sun Sep  2 23:32:56 2001
+++ mm/page_alloc.c        Sun Sep  2 23:34:03 2001
@@ -141,8 +141,8 @@
         * since it's nothing important, but we do want to make sure
         * it never gets negative.
         */
-       if (memory_pressure > NR_CPUS)
-               memory_pressure--;
+       if (memory_pressure > (NR_CPUS << order))
+               memory_pressure-= 1<<order;
 }

 #define MARK_USED(index, order, area) \
@@ -288,7 +288,7 @@
        /*
         * Allocations put pressure on the VM subsystem.
         */
-       memory_pressure++;
+       memory_pressure+= 1<<order;

        /*
         * (If anyone calls gfp from interrupts nonatomically then it

--
Alex Bligh