linux-kernel - [PATCHv9 09/32] thp: handle file pages in split_huge

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Date:	Mon,  6 Jun 2016 17:06:46 +0300
From:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:	Hugh Dickins <hughd@...gle.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Dave Hansen <dave.hansen@...el.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Christoph Lameter <cl@...two.org>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Jerome Marchand <jmarchan@...hat.com>,
	Yang Shi <yang.shi@...aro.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	Andres Lagar-Cavilla <andreslc@...gle.com>,
	Ning Qu <quning@...il.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCHv9 09/32] thp: handle file pages in split_huge_pmd()

Splitting THP PMD is simple: just unmap it as in DAX case. This way we
can avoid memory overhead on page table allocation to deposit.

It's probably a good idea to try to allocation page table with
GFP_ATOMIC in __split_huge_pmd_locked() to avoid refaulting the area,
but clearing pmd should be good enough for now.

Unlike DAX, we also remove the page from rmap and drop reference.
pmd_young() is transfered to PageReferenced().

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
---
 mm/huge_memory.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 2e838795aab1..6631c89b4bfc 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2995,10 +2995,18 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
 
 	count_vm_event(THP_SPLIT_PMD);
 
-	if (vma_is_dax(vma)) {
-		pmd_t _pmd = pmdp_huge_clear_flush_notify(vma, haddr, pmd);
+	if (!vma_is_anonymous(vma)) {
+		_pmd = pmdp_huge_clear_flush_notify(vma, haddr, pmd);
 		if (is_huge_zero_pmd(_pmd))
 			put_huge_zero_page();
+		if (vma_is_dax(vma))
+			return;
+		page = pmd_page(_pmd);
+		if (!PageReferenced(page) && pmd_young(_pmd))
+			SetPageReferenced(page);
+		page_remove_rmap(page, true);
+		put_page(page);
+		add_mm_counter(mm, MM_FILEPAGES, -HPAGE_PMD_NR);
 		return;
 	} else if (is_huge_zero_pmd(*pmd)) {
 		return __split_huge_zero_page_pmd(vma, haddr, pmd);
-- 
2.8.1