Re: [PATCH v5 04/13] mm/shmem: Restrict MFD_INACCESSIBLE memory against RLIMIT_MEMLOCK

[Chao Peng]

On Tue, Apr 12, 2022 at 10:28:21PM +0300, Kirill A. Shutemov wrote:
> On Tue, Apr 12, 2022 at 09:39:25PM +0800, Chao Peng wrote:
> > On Mon, Apr 11, 2022 at 06:32:33PM +0300, Kirill A. Shutemov wrote:
> > > On Thu, Apr 07, 2022 at 04:05:36PM +0000, Sean Christopherson wrote:
> > > > Hmm, shmem_writepage() already handles SHM_F_INACCESSIBLE by rejecting 
> > > > the swap, so
> > > > maybe it's just the page migration path that needs to be updated?
> > > 
> > > My early version prevented migration with -ENOTSUPP for
> > > address_space_operations::migratepage().
> > > 
> > > What's wrong with that approach?
> > 
> > I previously thought migratepage will not be called since we already
> > marked the pages as UNMOVABLE, sounds not correct?
> 
> Do you mean missing __GFP_MOVABLE?

Yes.

> I can be wrong, but I don't see that it
> direclty affects if the page is migratable. It is a hint to page allocator
> to group unmovable pages to separate page block and impove availablity of
> higher order pages this way. Page allocator tries to allocate unmovable
> pages from pages blocks that already have unmovable pages.

OK, thanks.

Chao
> 
> -- 
>  Kirill A. Shutemov