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Date: Fri, 18 Jun 2004 13:40:45 -0700
From: Andrew Morton <akpm@osdl.org>
To: Dimitri Sivanich <sivanich@sgi.com>
Cc: manfred@colorfullife.com, linux-kernel@vger.kernel.org,
       lse-tech@lists.sourceforge.net, linux-mm@kvack.org
Subject: Re: [PATCH]: Option to run cache reap in thread mode
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Dimitri Sivanich <sivanich@sgi.com> wrote:
>
> At the time of the holdoff (the point where we've spent a total of 30 usec in
> the timer_interrupt), we've looped through more than 100 of the 131 caches,
> usually closer to 120.

ahh, ooh, ow, of course.

Manfred, we need a separate list of "slabs which might need reaping".

That'll help the average case.  To help the worst case we should change
cache_reap() to only reap (say) ten caches from the head of the new list
and to then return.  Maybe increase the timer frequency too.

something like:

/*
 * FIFO list of caches (via kmem_cache_t.reap_list) which need consideration in
 * cache_reap().  Protected by cache_chain_sem.
 */
static LIST_HEAD(global_reap_list);

cache_reap()
{
	for (i = 0; i < 10; i++) {
		if (list_empty(&global_reap_list))
			break;
		cachep = list_entry(&global_reap_list, kmem_cache_t, reap_list);
		list_del_init(&cachep->reap_list);
		<prune it>
	}
}

mark_cache_for_reaping(kmem_cach_t *cachep)
{
	if (list_empty(&cachep->reap_list)) {
		if (!down_trylock(&cache_chain_sem)) {
			list_add(&cachep->reap_list, &global_reap_list);
			up(&cache_chain_sem);
	}
}

Maybe cache_chain_sem should become a spinlock.
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