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Subject[PATCH 2/2] mm: swap: move anonymous THP split logic to vmscan
Date
The add_to_swap aims to allocate swap_space(ie, swap slot and
swapcache) so if it fails due to lack of space in case of THP
or something(hdd swap but tries THP swapout) *caller* rather
than add_to_swap itself should split the THP page and retry it
with base page which is more natural.

Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
include/linux/swap.h | 4 ++--
mm/swap_state.c | 23 ++++++-----------------
mm/vmscan.c | 17 ++++++++++++++++-
3 files changed, 24 insertions(+), 20 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 8f12f67e869f..87cca2169d44 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -359,7 +359,7 @@ extern struct address_space *swapper_spaces[];
>> SWAP_ADDRESS_SPACE_SHIFT])
extern unsigned long total_swapcache_pages(void);
extern void show_swap_cache_info(void);
-extern int add_to_swap(struct page *, struct list_head *list);
+extern int add_to_swap(struct page *);
extern int add_to_swap_cache(struct page *, swp_entry_t, gfp_t);
extern int __add_to_swap_cache(struct page *page, swp_entry_t entry);
extern void __delete_from_swap_cache(struct page *);
@@ -479,7 +479,7 @@ static inline struct page *lookup_swap_cache(swp_entry_t swp)
return NULL;
}

-static inline int add_to_swap(struct page *page, struct list_head *list)
+static inline int add_to_swap(struct page *page)
{
return 0;
}
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 0ad214d7a7ad..9c71b6b2562f 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -184,7 +184,7 @@ void __delete_from_swap_cache(struct page *page)
* Allocate swap space for the page and add the page to the
* swap cache. Caller needs to hold the page lock.
*/
-int add_to_swap(struct page *page, struct list_head *list)
+int add_to_swap(struct page *page)
{
swp_entry_t entry;
int err;
@@ -192,12 +192,12 @@ int add_to_swap(struct page *page, struct list_head *list)
VM_BUG_ON_PAGE(!PageLocked(page), page);
VM_BUG_ON_PAGE(!PageUptodate(page), page);

-retry:
entry = get_swap_page(page);
if (!entry.val)
- goto fail;
+ return 0;
+
if (mem_cgroup_try_charge_swap(page, entry))
- goto fail_free;
+ goto fail;

/*
* Radix-tree node allocations from PF_MEMALLOC contexts could
@@ -218,23 +218,12 @@ int add_to_swap(struct page *page, struct list_head *list)
* add_to_swap_cache() doesn't return -EEXIST, so we can safely
* clear SWAP_HAS_CACHE flag.
*/
- goto fail_free;
-
- if (PageTransHuge(page)) {
- err = split_huge_page_to_list(page, list);
- if (err) {
- delete_from_swap_cache(page);
- return 0;
- }
- }
+ goto fail;

return 1;

-fail_free:
- put_swap_page(page, entry);
fail:
- if (PageTransHuge(page) && !split_huge_page_to_list(page, list))
- goto retry;
+ put_swap_page(page, entry);
return 0;
}

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 57268c0c8fcf..767e20856080 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1125,8 +1125,23 @@ static unsigned long shrink_page_list(struct list_head *page_list,
!PageSwapCache(page)) {
if (!(sc->gfp_mask & __GFP_IO))
goto keep_locked;
- if (!add_to_swap(page, page_list))
+ if (!add_to_swap(page)) {
+ if (!PageTransHuge(page))
+ goto activate_locked;
+ /* Split THP and swap individual base pages */
+ if (split_huge_page_to_list(page, page_list))
+ goto activate_locked;
+ if (!add_to_swap(page))
+ goto activate_locked;
+ }
+
+ /* XXX: We don't support THP writes */
+ if (PageTransHuge(page) &&
+ split_huge_page_to_list(page, page_list)) {
+ delete_from_swap_cache(page);
goto activate_locked;
+ }
+
may_enter_fs = 1;

/* Adding to swap updated mapping */
--
2.7.4
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