Re: [PATCH] Fix do_mlock so page alignment is to hugepage boundries when needed

[Hugh Dickins <hugh@veritas.com>]

On Wed, 17 May 2006, Eric Paris wrote:
> 
> This patch still solves the problem of the kernel currently being more
> restrictive on what we accept from userspace for the length of the mlock
> if it is a hugepage rather than a regular page.  With a regular page we
> will round the value from userspace and happily go about our business of
> mlocking.  For a hugepage it just rejects it if userspace doesn't align
> it themselves.  This allows the kernel to do the same work for hugepages
> that it does for normal pages.

You do have a point that there's an inconsistency there.  But we could
argue a long time what's inconsistent with what - I'd say it's mlock
being inconsistent with mprotect, munmap, msync, madvise, etc.  I
don't see an outright reason to change from the current behaviour.

You do realize that there's almost no point in mlocking a hugepage area
anyway?  (I wrote that first without the "almost", but now with hugepage
faulting, it does provide another way to fault in all the pages at once.)

Hugh