Re: Strange dcache memory pressure when highmem enabled

[Andrew Morton <akpm@osdl.org>]

Neil Brown <neilb@cse.unsw.edu.au> wrote:
>
> I noticed that shrink_caches calls shrink_dcache_memory independant
>   of the classzone that is being shrunk.  So if we are trying to
>   shrink ZONE_HIGHMEM, the dentry_cache is shrunk, even though the
>   dentry_cache doesn't live in highmem.  However I'm not sure if I have
>   understood the classzones well enough for that observation even to
>   make sense.

Makes heaps of sense.  Here's an instabackport of what we did in 2.6:

 mm/vmscan.c |   12 +++++++++---
 1 files changed, 9 insertions(+), 3 deletions(-)

diff -puN mm/vmscan.c~a mm/vmscan.c
--- 24/mm/vmscan.c~a	2003-10-14 22:41:34.000000000 -0700
+++ 24-akpm/mm/vmscan.c	2003-10-14 22:42:22.000000000 -0700
@@ -640,11 +640,17 @@ int try_to_free_pages_zone(zone_t *class
 			nr_pages = shrink_caches(classzone, gfp_mask, nr_pages, &failed_swapout);
 			if (nr_pages <= 0)
 				return 1;
-			shrink_dcache_memory(vm_vfs_scan_ratio, gfp_mask);
-			shrink_icache_memory(vm_vfs_scan_ratio, gfp_mask);
+			if (classzone - classzone->zone_pgdat->node_zones <
+						ZONE_HIGHMEM) {
+				shrink_dcache_memory(vm_vfs_scan_ratio,
+							gfp_mask);
+				shrink_icache_memory(vm_vfs_scan_ratio,
+							gfp_mask);
 #ifdef CONFIG_QUOTA
-			shrink_dqcache_memory(vm_vfs_scan_ratio, gfp_mask);
+				shrink_dqcache_memory(vm_vfs_scan_ratio,
+							gfp_mask);
 #endif
+			}
 			if (!failed_swapout)
 				failed_swapout = !swap_out(classzone);
 		} while (--tries);

_