Re: [PATCH 2/2] mm: swap: move anonymous THP split logic to vmscan

[Johannes Weiner]

On Fri, May 12, 2017 at 11:21:24AM +0900, Minchan Kim wrote:
> 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 
> Signed-off-by: Minchan Kim 

Acked-by: Johannes Weiner 

Re: [PATCH 2/2] mm: swap: move anonymous THP split logic to vmscan

[Johannes Weiner]

On Fri, May 12, 2017 at 11:21:24AM +0900, Minchan Kim wrote:
> 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 
> Signed-off-by: Minchan Kim 

Acked-by: Johannes Weiner 

[PATCH 2/2] mm: swap: move anonymous THP split logic to vmscan

[Minchan Kim]

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 
Signed-off-by: Minchan Kim 
---
 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

[PATCH 2/2] mm: swap: move anonymous THP split logic to vmscan

[Minchan Kim]

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 
Signed-off-by: Minchan Kim 
---
 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