[PATCH] Allocate correct amount of memory for pid hash

[Anton Blanchard]

Hi Nick,

> Use hlists for the PID hashes. This halves the memory footprint of these
> hashes. No benchmarks, but I think this is a worthy improvement because
> the hashes are something that would be likely to have significant portions
> loaded into the cache of every CPU on some workloads.
> 
> This comes at the "expense" of
> 	1. reintroducing the memory  prefetch into the hash traversal loop;
> 	2. adding new pids to the head of the list instead of the tail. I
> 	   suspect that if this was a big problem then the hash isn't sized
> 	   well or could benefit from moving hot entries to the head.
> 
> Also, account for all the pid hashes when reporting hash memory usage.

It looks like we are now allocating twice as much memory as required.
How does this look?

Signed-off-by: Anton Blanchard <anton@xxxxxxxxx>

diff -puN kernel/pid.c~fix_freemem_reporting kernel/pid.c
--- foobar2/kernel/pid.c~fix_freemem_reporting	2004-09-06 21:17:34.185012321 +1000
+++ foobar2-anton/kernel/pid.c	2004-09-06 21:25:29.494818586 +1000
@@ -278,7 +278,7 @@ void __init pidhash_init(void)
 
 	for (i = 0; i < PIDTYPE_MAX; i++) {
 		pid_hash[i] = alloc_bootmem(pidhash_size *
-					sizeof(struct list_head));
+					sizeof(struct hlist_head));
 		if (!pid_hash[i])
 			panic("Could not alloc pidhash!\n");
 		for (j = 0; j < pidhash_size; j++)
_
-
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