From mboxrd@z Thu Jan  1 00:00:00 1970
From: erik quanstrom <quanstro@quanstro.net>
Date: Wed, 11 Jun 2014 14:04:33 -0400
To: 9fans@9fans.net
Message-ID: <8977d7fab2c905e43577db135dc59751@brasstown.quanstro.net>
In-Reply-To: <055f6bc9f00c19e6b8a81c434408e6e3@brasstown.quanstro.net>
References: <bbc4961fb4a4dcd9cc4ebbaf0e11cb8f@felloff.net>
	<055f6bc9f00c19e6b8a81c434408e6e3@brasstown.quanstro.net>
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Subject: Re: [9fans] duppage
Topicbox-Message-UUID: f96e9756-ead8-11e9-9d60-3106f5b1d025

On Sun Jun  8 14:17:16 EDT 2014, quanstro@quanstro.net wrote:
> On Sun Jun  8 13:55:52 EDT 2014, cinap_lenrek@felloff.net wrote:
> > right. the question is, how did it vanish from the image cache.
>
> i think it is in the image cache, but .ref >1.

perhaps independent of your question,
my assumption is correct, and proven.

the problem was that pagereclaim() only looked through
pga.pgsza[0], but since 2MiB pages were introduced in nix,
no pages could ever be reclaimed this way, since they would
be in pga.pgsza[1].

i don't think this really addresses your question, or my
original problem though.  the corrected version which i think
should work for any architecture is below.  i intend to
incorporate charles locking changes later on.
(lock(&lga.pgsza[lg]) instead of the whole thing.)
i think those changes (in the 9atom /sys/src/9 kernels)
are good stuff.

- erik
---
/*
 * Called from imagereclaim, to try to release Images.
 * The (ignored) argument indicates a preferred image for release.
 */
void
pagereclaim(Image*)
{
	int lg, n;
	usize sz;
	Page *p;

	lock(&pga);

	/*
	 * All the pages with images backing them are at the
	 * end of the list (see putpage) so start there and work
	 * backward.  Assume the smallest page size (BOTCH).
	 */
	sz = 0;
	n = 0;
	for(lg = 0; lg < m->npgsz; lg++)
		for(p = pga.pgsza[lg].tail; p != nil; p = p->prev){
			if(p->image != nil && p->ref == 0 && canlock(p)){
				if(p->ref == 0) {
					n++;
					sz += 1<<m->pgszlg2[lg];
					uncachepage(p);
				}
			unlock(p);
			if(sz >= 20*MiB && n>5)
				break;
		}
	}
	unlock(&pga);
}