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

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Message-ID: <CAJd=RBBL7VV50zHP2obJ7_CzOekgH9i-E3Fz3PO5YXk5f=B2Kw@mail.gmail.com>
Date:	Fri, 15 Mar 2013 21:55:25 +0800
From:	Hillf Danton <dhillf@...il.com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:	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

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.
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