linux-kernel - Re: [PATCHv2, RFC 08/30] thp, mm: rewrite add_to_page_cache

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Message-Id: <20130315150522.8BF97E0085@blue.fi.intel.com>
Date:	Fri, 15 Mar 2013 17:05:22 +0200 (EET)
From:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:	Hillf Danton <dhillf@...il.com>
Cc:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Hugh Dickins <hughd@...gle.com>,
	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 <matthew.r.wilcox@...el.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2, RFC 08/30] thp, mm: rewrite add_to_page_cache_locked()
 to support huge pages

Hillf Danton wrote:
> On Fri, Mar 15, 2013 at 9:50 PM, Kirill A. Shutemov
> <kirill.shutemov@...ux.intel.com> wrote:
> > Hillf Danton wrote:
> >> On Fri, Mar 15, 2013 at 9:23 PM, Kirill A. Shutemov
> >> <kirill.shutemov@...ux.intel.com> wrote:
> >> > Hillf Danton wrote:
> >> >> On Fri, Mar 15, 2013 at 1:50 AM, Kirill A. Shutemov
> >> >> <kirill.shutemov@...ux.intel.com> wrote:
> >> >> > +       page_cache_get(page);
> >> >> > +       spin_lock_irq(&mapping->tree_lock);
> >> >> > +       page->mapping = mapping;
> >> >> > +       page->index = offset;
> >> >> > +       error = radix_tree_insert(&mapping->page_tree, offset, page);
> >> >> > +       if (unlikely(error))
> >> >> > +               goto err;
> >> >> > +       if (PageTransHuge(page)) {
> >> >> > +               int i;
> >> >> > +               for (i = 1; i < HPAGE_CACHE_NR; i++) {
> >> >>                       struct page *tail = page + i; to easy reader
> >> >>
> >> >> > +                       page_cache_get(page + i);
> >> >> s/page_cache_get/get_page_foll/ ?
> >> >
> >> > Why?
> >> >
> >> see follow_trans_huge_pmd() please.
> >
> > Sorry, I fail to see how follow_trans_huge_pmd() is relevant here.
> > Could you elaborate?
> >
> Lets see the code
> 
> 	page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
> //page is tail now
> 	VM_BUG_ON(!PageCompound(page));
> 	if (flags & FOLL_GET)
> 		get_page_foll(page);
> //raise page count with the foll function
> 
> thus I raised question.

get_page_foll() is designed to be part of follow_page*() call chain.
get_page() can handle compound pages properly.

-- 
 Kirill A. Shutemov
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