linux-kernel - Re: [PATCH] mm: swap prefetch more improvements

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20070514160123.4b1ab108.akpm@linux-foundation.org>
Date:	Mon, 14 May 2007 16:01:23 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Con Kolivas <kernel@...ivas.org>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	ck@....kolivas.org
Subject: Re: [PATCH] mm: swap prefetch more improvements

On Tue, 15 May 2007 08:43:35 +1000
Con Kolivas <kernel@...ivas.org> wrote:

> On Tuesday 15 May 2007 08:00, Andrew Morton wrote:
> > On Mon, 14 May 2007 10:50:54 +1000
> >
> > Con Kolivas <kernel@...ivas.org> wrote:
> > > akpm, please queue on top of "mm: swap prefetch improvements"
> > >
> > > ---
> > > Failed radix_tree_insert wasn't being handled leaving stale kmem.
> > >
> > > The list should be iterated over in the reverse order when prefetching.
> > >
> > > Make the yield within kprefetchd stronger through the use of
> > > cond_resched.
> >
> > hm.
> >
> > > -		might_sleep();
> > > -		if (!prefetch_suitable())
> > > +		/* Yield to anything else running */
> > > +		if (cond_resched() || !prefetch_suitable())
> > >  			goto out_unlocked;
> >
> > So if cond_resched() happened to schedule away, we terminate this
> > swap-tricking attempt.  It's not possible to determine the reasons for this
> > from the code or from the changelog (==bad).
> >
> > How come?
> 
> Hmm I thought the line above that says "yield to anything else running" was 
> explicit enough. The idea is kprefetchd shouldn't run if any other real 
> activity is happening just about anywhere, and a positive cond_resched would 
> indicate likely activity so we just put kprefetchd back to sleep.

But kprefetchd runs as SCHED_BATCH.  Doesn't that mean that some low-prio
background thing (seti?) will disable swap-prefetch?

I mean, if swap-prefetch is actually useful, then it'll still be useful if
the machine happens to be doing some computational work.  It's not obvious
to me that there is linkage between "doing CPU work" and "prefetching is
presently undesirable".


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/