linux-kernel - Re: [PATCH 07/12] mm, thp, tmpfs: handle huge page in shmem_undo

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Message-Id: <20131016120951.B5012E0090@blue.fi.intel.com>
Date:	Wed, 16 Oct 2013 15:09:51 +0300 (EEST)
From:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:	Ning Qu <quning@...gle.com>
Cc:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Wu Fengguang <fengguang.wu@...el.com>, Jan Kara <jack@...e.cz>,
	Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org,
	Andi Kleen <ak@...ux.intel.com>,
	Matthew Wilcox <willy@...ux.intel.com>,
	Hillf Danton <dhillf@...il.com>, Dave Hansen <dave@...1.net>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 07/12] mm, thp, tmpfs: handle huge page in
 shmem_undo_range for truncate

Ning Qu wrote:
> > Again. Here and below ifdef is redundant: PageTransHugeCache() is zero
> > compile-time and  thp case will be optimize out.
> 
> The problem is actually from HPAGE_CACHE_INDEX_MASK, it is marked as
> build bug when CONFIG_TRANSPARENT_HUGEPAGE_PAGECACHE is false. So we
> either wrap some logic inside a inline function, or we have to be like
> this .. Or we don't treat the HPAGE_CACHE_INDEX_MASK as a build bug?

HPAGE_CACHE_INDEX_MASK shouldn't be a problem.
If it's wrapped into 'if PageTransHugeCache(page)' or similar it will be
eliminated by compiler if thp-pc disabled and build bug will not be
triggered.

> 
> >
> > And do we really need a copy of truncate logic here? Is there a way to
> > share code?
> >
> The truncate between tmpfs and general one is similar but not exactly
> the same (no readahead), so share the whole function might not be a
> good choice from the perspective of tmpfs? Anyway, there are other
> similar functions in tmpfs, e.g. the one you mentioned for
> shmem_add_to_page_cache. It is possible to share the code, I am just
> worried it will make the logic more complicated?

I think introducing thp-pc is good opportunity to refactor all these code.

-- 
 Kirill A. Shutemov
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