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From:   Zi Yan <ziy@nvidia.com>
To:     <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>
CC:     Dave Hansen <dave.hansen@linux.intel.com>,
        Michal Hocko <mhocko@kernel.org>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
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        Mel Gorman <mgorman@techsingularity.net>,
        John Hubbard <jhubbard@nvidia.com>,
        Mark Hairgrove <mhairgrove@nvidia.com>,
        Nitin Gupta <nigupta@nvidia.com>,
        David Nellans <dnellans@nvidia.com>, Zi Yan <ziy@nvidia.com>
Subject: [RFC PATCH 02/31] mm: migrate: Add THP exchange support.
Date:   Fri, 15 Feb 2019 14:03:05 -0800
Message-ID: <20190215220334.29298-3-ziy@nvidia.com>
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Add support for exchange between two THPs.

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
 mm/exchange.c | 47 ++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 38 insertions(+), 9 deletions(-)

diff --git a/mm/exchange.c b/mm/exchange.c
index a607348cc6f4..8cf286fc0f10 100644
--- a/mm/exchange.c
+++ b/mm/exchange.c
@@ -48,7 +48,8 @@ struct page_flags {
 	unsigned int page_swapcache:1;
 	unsigned int page_writeback:1;
 	unsigned int page_private:1;
-	unsigned int __pad:3;
+	unsigned int page_doublemap:1;
+	unsigned int __pad:2;
 };
=20
=20
@@ -125,20 +126,23 @@ static void exchange_huge_page(struct page *dst, stru=
ct page *src)
 static void exchange_page_flags(struct page *to_page, struct page *from_pa=
ge)
 {
 	int from_cpupid, to_cpupid;
-	struct page_flags from_page_flags, to_page_flags;
+	struct page_flags from_page_flags =3D {0}, to_page_flags =3D {0};
 	struct mem_cgroup *to_memcg =3D page_memcg(to_page),
 					  *from_memcg =3D page_memcg(from_page);
=20
 	from_cpupid =3D page_cpupid_xchg_last(from_page, -1);
=20
-	from_page_flags.page_error =3D TestClearPageError(from_page);
+	from_page_flags.page_error =3D PageError(from_page);
+	if (from_page_flags.page_error)
+		ClearPageError(from_page);
 	from_page_flags.page_referenced =3D TestClearPageReferenced(from_page);
 	from_page_flags.page_uptodate =3D PageUptodate(from_page);
 	ClearPageUptodate(from_page);
 	from_page_flags.page_active =3D TestClearPageActive(from_page);
 	from_page_flags.page_unevictable =3D TestClearPageUnevictable(from_page);
 	from_page_flags.page_checked =3D PageChecked(from_page);
-	ClearPageChecked(from_page);
+	if (from_page_flags.page_checked)
+		ClearPageChecked(from_page);
 	from_page_flags.page_mappedtodisk =3D PageMappedToDisk(from_page);
 	ClearPageMappedToDisk(from_page);
 	from_page_flags.page_dirty =3D PageDirty(from_page);
@@ -148,18 +152,22 @@ static void exchange_page_flags(struct page *to_page,=
 struct page *from_page)
 	clear_page_idle(from_page);
 	from_page_flags.page_swapcache =3D PageSwapCache(from_page);
 	from_page_flags.page_writeback =3D test_clear_page_writeback(from_page);
+	from_page_flags.page_doublemap =3D PageDoubleMap(from_page);
=20
=20
 	to_cpupid =3D page_cpupid_xchg_last(to_page, -1);
=20
-	to_page_flags.page_error =3D TestClearPageError(to_page);
+	to_page_flags.page_error =3D PageError(to_page);
+	if (to_page_flags.page_error)
+		ClearPageError(to_page);
 	to_page_flags.page_referenced =3D TestClearPageReferenced(to_page);
 	to_page_flags.page_uptodate =3D PageUptodate(to_page);
 	ClearPageUptodate(to_page);
 	to_page_flags.page_active =3D TestClearPageActive(to_page);
 	to_page_flags.page_unevictable =3D TestClearPageUnevictable(to_page);
 	to_page_flags.page_checked =3D PageChecked(to_page);
-	ClearPageChecked(to_page);
+	if (to_page_flags.page_checked)
+		ClearPageChecked(to_page);
 	to_page_flags.page_mappedtodisk =3D PageMappedToDisk(to_page);
 	ClearPageMappedToDisk(to_page);
 	to_page_flags.page_dirty =3D PageDirty(to_page);
@@ -169,6 +177,7 @@ static void exchange_page_flags(struct page *to_page, s=
truct page *from_page)
 	clear_page_idle(to_page);
 	to_page_flags.page_swapcache =3D PageSwapCache(to_page);
 	to_page_flags.page_writeback =3D test_clear_page_writeback(to_page);
+	to_page_flags.page_doublemap =3D PageDoubleMap(to_page);
=20
 	/* set to_page */
 	if (from_page_flags.page_error)
@@ -195,6 +204,8 @@ static void exchange_page_flags(struct page *to_page, s=
truct page *from_page)
 		set_page_young(to_page);
 	if (from_page_flags.page_is_idle)
 		set_page_idle(to_page);
+	if (from_page_flags.page_doublemap)
+		SetPageDoubleMap(to_page);
=20
 	/* set from_page */
 	if (to_page_flags.page_error)
@@ -221,6 +232,8 @@ static void exchange_page_flags(struct page *to_page, s=
truct page *from_page)
 		set_page_young(from_page);
 	if (to_page_flags.page_is_idle)
 		set_page_idle(from_page);
+	if (to_page_flags.page_doublemap)
+		SetPageDoubleMap(from_page);
=20
 	/*
 	 * Copy NUMA information to the new page, to prevent over-eager
@@ -280,6 +293,7 @@ static int exchange_page_move_mapping(struct address_sp=
ace *to_mapping,
=20
 	VM_BUG_ON_PAGE(to_mapping !=3D page_mapping(to_page), to_page);
 	VM_BUG_ON_PAGE(from_mapping !=3D page_mapping(from_page), from_page);
+	VM_BUG_ON(PageCompound(from_page) !=3D PageCompound(to_page));
=20
 	if (!to_mapping) {
 		/* Anonymous page without mapping */
@@ -600,7 +614,6 @@ static int unmap_and_exchange(struct page *from_page,
 	to_mapping =3D to_page->mapping;
 	from_index =3D from_page->index;
 	to_index =3D to_page->index;
-
 	/*
 	 * Corner case handling:
 	 * 1. When a new swap-cache page is read into, it is added to the LRU
@@ -691,6 +704,23 @@ static int unmap_and_exchange(struct page *from_page,
 	return rc;
 }
=20
+static bool can_be_exchanged(struct page *from, struct page *to)
+{
+	if (PageCompound(from) !=3D PageCompound(to))
+		return false;
+
+	if (PageHuge(from) !=3D PageHuge(to))
+		return false;
+
+	if (PageHuge(from) || PageHuge(to))
+		return false;
+
+	if (compound_order(from) !=3D compound_order(to))
+		return false;
+
+	return true;
+}
+
 /*
  * Exchange pages in the exchange_list
  *
@@ -751,9 +781,8 @@ static int exchange_pages(struct list_head *exchange_li=
st,
 			continue;
 		}
=20
-		/* TODO: compound page not supported */
 		/* to_page can be file-backed page  */
-		if (PageCompound(from_page) ||
+		if (!can_be_exchanged(from_page, to_page) ||
 			page_mapping(from_page)
 			) {
 			++failed;
--=20
2.20.1