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Subject[RFC PATCH 02/31] mm: migrate: Add THP exchange support.
Date
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;
};


@@ -125,20 +126,23 @@ static void exchange_huge_page(struct page *dst, struct page *src)
static void exchange_page_flags(struct page *to_page, struct page *from_page)
{
int from_cpupid, to_cpupid;
- struct page_flags from_page_flags, to_page_flags;
+ struct page_flags from_page_flags = {0}, to_page_flags = {0};
struct mem_cgroup *to_memcg = page_memcg(to_page),
*from_memcg = page_memcg(from_page);

from_cpupid = page_cpupid_xchg_last(from_page, -1);

- from_page_flags.page_error = TestClearPageError(from_page);
+ from_page_flags.page_error = PageError(from_page);
+ if (from_page_flags.page_error)
+ ClearPageError(from_page);
from_page_flags.page_referenced = TestClearPageReferenced(from_page);
from_page_flags.page_uptodate = PageUptodate(from_page);
ClearPageUptodate(from_page);
from_page_flags.page_active = TestClearPageActive(from_page);
from_page_flags.page_unevictable = TestClearPageUnevictable(from_page);
from_page_flags.page_checked = PageChecked(from_page);
- ClearPageChecked(from_page);
+ if (from_page_flags.page_checked)
+ ClearPageChecked(from_page);
from_page_flags.page_mappedtodisk = PageMappedToDisk(from_page);
ClearPageMappedToDisk(from_page);
from_page_flags.page_dirty = 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 = PageSwapCache(from_page);
from_page_flags.page_writeback = test_clear_page_writeback(from_page);
+ from_page_flags.page_doublemap = PageDoubleMap(from_page);


to_cpupid = page_cpupid_xchg_last(to_page, -1);

- to_page_flags.page_error = TestClearPageError(to_page);
+ to_page_flags.page_error = PageError(to_page);
+ if (to_page_flags.page_error)
+ ClearPageError(to_page);
to_page_flags.page_referenced = TestClearPageReferenced(to_page);
to_page_flags.page_uptodate = PageUptodate(to_page);
ClearPageUptodate(to_page);
to_page_flags.page_active = TestClearPageActive(to_page);
to_page_flags.page_unevictable = TestClearPageUnevictable(to_page);
to_page_flags.page_checked = PageChecked(to_page);
- ClearPageChecked(to_page);
+ if (to_page_flags.page_checked)
+ ClearPageChecked(to_page);
to_page_flags.page_mappedtodisk = PageMappedToDisk(to_page);
ClearPageMappedToDisk(to_page);
to_page_flags.page_dirty = PageDirty(to_page);
@@ -169,6 +177,7 @@ static void exchange_page_flags(struct page *to_page, struct page *from_page)
clear_page_idle(to_page);
to_page_flags.page_swapcache = PageSwapCache(to_page);
to_page_flags.page_writeback = test_clear_page_writeback(to_page);
+ to_page_flags.page_doublemap = PageDoubleMap(to_page);

/* set to_page */
if (from_page_flags.page_error)
@@ -195,6 +204,8 @@ static void exchange_page_flags(struct page *to_page, struct 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);

/* set from_page */
if (to_page_flags.page_error)
@@ -221,6 +232,8 @@ static void exchange_page_flags(struct page *to_page, struct 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);

/*
* Copy NUMA information to the new page, to prevent over-eager
@@ -280,6 +293,7 @@ static int exchange_page_move_mapping(struct address_space *to_mapping,

VM_BUG_ON_PAGE(to_mapping != page_mapping(to_page), to_page);
VM_BUG_ON_PAGE(from_mapping != page_mapping(from_page), from_page);
+ VM_BUG_ON(PageCompound(from_page) != PageCompound(to_page));

if (!to_mapping) {
/* Anonymous page without mapping */
@@ -600,7 +614,6 @@ static int unmap_and_exchange(struct page *from_page,
to_mapping = to_page->mapping;
from_index = from_page->index;
to_index = 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;
}

+static bool can_be_exchanged(struct page *from, struct page *to)
+{
+ if (PageCompound(from) != PageCompound(to))
+ return false;
+
+ if (PageHuge(from) != PageHuge(to))
+ return false;
+
+ if (PageHuge(from) || PageHuge(to))
+ return false;
+
+ if (compound_order(from) != 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_list,
continue;
}

- /* 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;
--
2.20.1
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