[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <200706071030.15317.jesse.barnes@intel.com>
Date: Thu, 7 Jun 2007 10:30:14 -0700
From: Jesse Barnes <jesse.barnes@...el.com>
To: "Eric W. Biederman" <ebiederm@...ssion.com>
Cc: Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
Justin Piszcz <jpiszcz@...idpixels.com>
Subject: Re: [PATCH] trim memory not covered by WB MTRRs
On Thursday, June 7, 2007 12:45 am Eric W. Biederman wrote:
> Ok. Overall this feels good but a few nits below.
> Would it make sense to split this into two patches.
> The first to just do the cleanup that removes the allocations
> for holding the mttr ranges?
I suppose we could split it, but it's small, and the only reason for
removing the allocations was so that we could init it earlier.
> > struct mtrr_state {
> > - struct mtrr_var_range *var_ranges;
> > + struct mtrr_var_range var_ranges[NUM_VAR_RANGES];
>
> Could we name it MAX_VAR_RANGES and not NUM_VAR_RANGES.
> In practices this is going to be 8 for every cpu I know of,
> so calling this NUM_VAR_RANGES may be a little confusing.
You're right, I should have kept the old name with MAX_ in it. I'll fix
it up.
> > /* RED-PEN: this is accessed without any locking */
> > -extern unsigned int *usage_table;
> > +extern unsigned int usage_table[];
>
> I think that should be:
> > +extern unsigned int usage_table[NUM_VAR_RANGES];
>
> Or even better yet the declaration moved to a header file.
Oops, yeah, this should just be in mtrr.h.
> This looks like it will handle the common case, so I have no major
> objections to this code.
>
> At least in theory and possibly in practice there are a couple of
> corner cases we have missed her.
>
> - Overlapping MTRRs.
Overlapping should be ok, since that's usually intentional (e.g. one big
wb range with a portion of uc space due to another mtrr).
> - What happens if we have uncached memory lower down?
Holes definitely aren't dealt with, but then we haven't seen any yet...
> Except for performance problems I guess that case is relatively
> harmless. - Is it possible and worth it to amend the e820 map, so it
> shows the problem area as Reserved or otherwise not usable RAM?
That would be useful, but only if we moved the check to a little
earlier, prior to the addition of the active ranges from the e820.
Might be a little nicer than adjusting end_pfn, but will ultimately
achieve the same thing...
Jesse
-
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/
Powered by blists - more mailing lists