Re: sysfs interface to transparent hugepages

[Ben Hutchings <ben@decadent.org.uk>]

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On Mon, 2011-03-21 at 15:08 +0100, Andrea Arcangeli wrote:
> On Mon, Mar 21, 2011 at 01:13:03PM +0000, Ben Hutchings wrote:
> > You have tristates {never, madvise, always} for various THM features.
> > Internally, these are represented as a pair of flags.  They are exposed
> > through sysfs as tristates, but then they are also exposed as flags.
> 
> They must be bitflags for performance and cacheline saving reasons in
> the kernel (1 bitflag not enough in kernel for a userland
> tristate). They're more intuitive as tristate in the same file for the
> user to set (some combination of these flags is forbidden so exposing
> the flags to the user doesn't sound good idea, also considering it's
> an internal representation which may change, keeping the two separated
> is best, especially if you want your current lib not to break).
[...]

I understand all that.  However when I first looked at this I somehow
thought that the tristate values were *also* exposed as flags, but I was
mistaken.  Sorry to bother you with this non-issue.

Ben.

-- 
Ben Hutchings
Once a job is fouled up, anything done to improve it makes it worse.

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