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

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Date:   Mon, 3 Dec 2018 08:15:38 -0800
From:   Daniel Jordan <daniel.m.jordan@...cle.com>
To:     "Huang, Ying" <ying.huang@...el.com>
Cc:     Daniel Jordan <daniel.m.jordan@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Michal Hocko <mhocko@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Shaohua Li <shli@...nel.org>, Hugh Dickins <hughd@...gle.com>,
        Minchan Kim <minchan@...nel.org>,
        Rik van Riel <riel@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Zi Yan <zi.yan@...rutgers.edu>
Subject: Re: [PATCH -V7 RESEND 08/21] swap: Support to read a huge swap
 cluster for swapin a THP

On Sat, Dec 01, 2018 at 08:34:06AM +0800, Huang, Ying wrote:
> Daniel Jordan <daniel.m.jordan@...cle.com> 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.