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Date: Mon, 3 Dec 2018 08:15:38 -0800
From: Daniel Jordan <daniel.m.jordan@oracle.com>
Subject: Re: [PATCH -V7 RESEND 08/21] swap: Support to read a huge swap
 cluster for swapin a THP
Message-ID: <20181203161538.gxleg2ugdj2woadr@ca-dmjordan1.us.oracle.com>
References: <20181120085449.5542-1-ying.huang@intel.com>
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 <20181130233201.6yuzbhymtjddvf3u@ca-dmjordan1.us.oracle.com>
 <8736rirsox.fsf@yhuang-dev.intel.com>
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To: "Huang, Ying" <ying.huang@intel.com>
Cc: Daniel Jordan <daniel.m.jordan@oracle.com>, Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, Andrea Arcangeli <aarcange@redhat.com>, Michal Hocko <mhocko@kernel.org>, Johannes Weiner <hannes@cmpxchg.org>, Shaohua Li <shli@kernel.org>, Hugh Dickins <hughd@google.com>, Minchan Kim <minchan@kernel.org>, Rik van Riel <riel@redhat.com>, Dave Hansen <dave.hansen@linux.intel.com>, Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>, Zi Yan <zi.yan@cs.rutgers.edu>

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