Re: [PATCH -V7 RESEND 08/21] swap: Support to read a huge swap cluster for swapin a THP

[Daniel Jordan]

On Sat, Dec 01, 2018 at 08:34:06AM +0800, Huang, Ying wrote:
> Daniel Jordan <daniel.m.jordan@xxxxxxxxxx> writes:
> > What do you think?
> 
> I think that swapoff() which is the main user of try_to_unuse() isn't a
> common operation in practical.  So it's not necessary to make it more
> complex for this.

Ok, probably not worth the surgery on try_to_unuse, even if swapoff can be
expensive when it does happen.

> In alloc_hugepage_direct_gfpmask(), the only information provided by vma
> is: vma->flags & VM_HUGEPAGE.  Because we have no vma available, I think
> it is OK to just assume that the flag is cleared.  That is, rely on
> system-wide THP settings only.
> 
> What do you think about this proposal?

Sounds like a good compromise.

So alloc_hugepage_direct_gfpmask will learn to make 'vma' optional?  Slightly
concerned that future callers that should be passing vma's might not and open a
way to ignore vma huge page hints, but probably not a big deal in practice.