linux-kernel - Re: [RFC PATCH 0/2] Add hstate parameter to huge_pte

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Date:   Fri, 24 Mar 2017 13:37:09 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     Punit Agrawal <punit.agrawal@....com>, linux-mm@...ck.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Tyler Baicar <tbaicar@...eaurora.org>
Subject: Re: [RFC PATCH 0/2] Add hstate parameter to huge_pte_offset()

On Thu, Mar 23, 2017 at 01:55:27PM -0700, Mike Kravetz wrote:
> On 03/23/2017 05:58 AM, Punit Agrawal wrote:
> > On architectures that support hugepages composed of contiguous pte as
> > well as block entries at the same level in the page table,
> > huge_pte_offset() is not able to determine the right offset to return
> > when it encounters a swap entry (which is used to mark poisoned as
> > well as migrated pages in the page table).
> > 
> > huge_pte_offset() needs to know the size of the hugepage at the
> > requested address to determine the offset to return - the current
> > entry or the first entry of a set of contiguous hugepages. This came
> > up while enabling support for memory failure handling on arm64[0].
> > 
> > Patch 1 adds a hstate parameter to huge_pte_offset() to provide
> > additional information about the target address. It also updates the
> > signatures (and usage) of huge_pte_offset() for architectures that
> > override the generic implementation. This patch has been compile
> > tested on ia64 and x86.
> 
> I haven't looked at the performance implications of making huge_pte_offset
> just a little slower.  But, I think you can get hstate from the parameters
> passed today.
> 
> vma = find_vma(mm, addr);
> h = hstate_vma(vma);

It's better to avoid find_vma() in fast(?) path if possible. So passing it
down is probably better.

-- 
 Kirill A. Shutemov