Re: [PATCH] thp, mlock: update unevictable-lru.txt

["Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>]

On Tue, Mar 15, 2016 at 06:42:58PM +0300, Kirill A. Shutemov wrote:
> On Tue, Mar 15, 2016 at 08:30:54AM -0700, Dave Hansen wrote:
> > On 03/15/2016 07:55 AM, Kirill A. Shutemov wrote:
> > > +Transparent huge page is represented by single entry on a lru list and
> > > +therefore we can only make unevictable entire compound page, not
> > > +individual subpages.
> > 
> > A few grammar nits:
> > 
> > A transparent huge page is represented by a single entry on an lru list.
> > Therefore, we can only make unevictable an entire compound page, not
> > individual subpages.
> 
> Thanks.
> 
> > > +We handle this by forbidding mlocking PTE-mapped huge pages. This way we
> > > +keep the huge page accessible for vmscan. Under memory pressure the page
> > > +will be split, subpages from VM_LOCKED VMAs moved to unevictable lru and
> > > +the rest can be evicted.
> > 
> > What do you mean by "mlocking" in this context?  Do you mean that we
> > actually return -ESOMETHING from mlock() on PTE-mapped huge pages?  Or,
> > do you just mean that we defer treating PTE-mapped huge pages as
> > PageUnevictable() inside the kernel?
> 
> The latter.
> 
> > I think we should probably avoid saying "mlocking" when we really mean
> > "kernel-internal mlocked page handling" aka. the unevictable list.
> 
> What about
> 
> "We handle this by keeping PTE-mapped huge pages on normal LRU lists."
> 
> ?
> 
> The updated patch is below.

Err. That was the old patch.