Re: [PATCH v2 2/7] mm/swapfile.c: Replace some #ifdef with IS_ENABLED()
Dave Hansen writes:
> On 07/17/2018 08:25 PM, Huang, Ying wrote:
>>> Seriously, though, does it hurt us to add a comment or two to say
>>> something like:
>>>
>>> /*
>>> * Should not even be attempting cluster allocations when
>>> * huge page swap is disabled. Warn and fail the allocation.
>>> */
>>> if (!IS_ENABLED(CONFIG_THP_SWAP)) {
>>> VM_WARN_ON_ONCE(1);
>>> return 0;
>>> }
>> I totally agree with you that we should add more comments for THP swap
>> to improve the code readability. As for this specific case,
>> VM_WARN_ON_ONCE() here is just to capture some programming error during
>> development. Do we really need comments here?
>
> If it's code in mainline, we need to know what it is doing.
>
> If it's not useful to have in mainline, then let's remove it.
OK. Will add the comments.
Best Regards,
Huang, Ying
Re: [PATCH v2 2/7] mm/swapfile.c: Replace some #ifdef with IS_ENABLED()
Dave Hansen writes:
> On 07/17/2018 08:25 PM, Huang, Ying wrote:
>>> Seriously, though, does it hurt us to add a comment or two to say
>>> something like:
>>>
>>> /*
>>> * Should not even be attempting cluster allocations when
>>> * huge page swap is disabled. Warn and fail the allocation.
>>> */
>>> if (!IS_ENABLED(CONFIG_THP_SWAP)) {
>>> VM_WARN_ON_ONCE(1);
>>> return 0;
>>> }
>> I totally agree with you that we should add more comments for THP swap
>> to improve the code readability. As for this specific case,
>> VM_WARN_ON_ONCE() here is just to capture some programming error during
>> development. Do we really need comments here?
>
> If it's code in mainline, we need to know what it is doing.
>
> If it's not useful to have in mainline, then let's remove it.
OK. Will add the comments.
Best Regards,
Huang, Ying
Re: [PATCH v2 2/7] mm/swapfile.c: Replace some #ifdef with IS_ENABLED()
On 07/17/2018 08:25 PM, Huang, Ying wrote:
>> Seriously, though, does it hurt us to add a comment or two to say
>> something like:
>>
>> /*
>> * Should not even be attempting cluster allocations when
>> * huge page swap is disabled. Warn and fail the allocation.
>> */
>> if (!IS_ENABLED(CONFIG_THP_SWAP)) {
>> VM_WARN_ON_ONCE(1);
>> return 0;
>> }
> I totally agree with you that we should add more comments for THP swap
> to improve the code readability. As for this specific case,
> VM_WARN_ON_ONCE() here is just to capture some programming error during
> development. Do we really need comments here?
If it's code in mainline, we need to know what it is doing.
If it's not useful to have in mainline, then let's remove it.
Re: [PATCH v2 2/7] mm/swapfile.c: Replace some #ifdef with IS_ENABLED()
On 07/17/2018 08:25 PM, Huang, Ying wrote:
>> Seriously, though, does it hurt us to add a comment or two to say
>> something like:
>>
>> /*
>> * Should not even be attempting cluster allocations when
>> * huge page swap is disabled. Warn and fail the allocation.
>> */
>> if (!IS_ENABLED(CONFIG_THP_SWAP)) {
>> VM_WARN_ON_ONCE(1);
>> return 0;
>> }
> I totally agree with you that we should add more comments for THP swap
> to improve the code readability. As for this specific case,
> VM_WARN_ON_ONCE() here is just to capture some programming error during
> development. Do we really need comments here?
If it's code in mainline, we need to know what it is doing.
If it's not useful to have in mainline, then let's remove it.
Re: [PATCH v2 2/7] mm/swapfile.c: Replace some #ifdef with IS_ENABLED()
Dave Hansen writes:
>> @@ -878,6 +877,11 @@ static int swap_alloc_cluster(struct swap_info_struct
>> *si, swp_entry_t *slot)
>> unsigned long offset, i;
>> unsigned char *map;
>>
>> +if (!IS_ENABLED(CONFIG_THP_SWAP)) {
>> +VM_WARN_ON_ONCE(1);
>> +return 0;
>> +}
>
> I see you seized the opportunity to keep this code gloriously
> unencumbered by pesky comments. This seems like a time when you might
> have slipped up and been temped to add a comment or two. Guess not. :)
>
> Seriously, though, does it hurt us to add a comment or two to say
> something like:
>
> /*
>* Should not even be attempting cluster allocations when
>* huge page swap is disabled. Warn and fail the allocation.
>*/
> if (!IS_ENABLED(CONFIG_THP_SWAP)) {
> VM_WARN_ON_ONCE(1);
> return 0;
> }
I totally agree with you that we should add more comments for THP swap
to improve the code readability. As for this specific case,
VM_WARN_ON_ONCE() here is just to capture some programming error during
development. Do we really need comments here?
I will try to add more comments for other places in code regardless this
one.
Best Regards,
Huang, Ying
Re: [PATCH v2 2/7] mm/swapfile.c: Replace some #ifdef with IS_ENABLED()
Dave Hansen writes:
>> @@ -878,6 +877,11 @@ static int swap_alloc_cluster(struct swap_info_struct
>> *si, swp_entry_t *slot)
>> unsigned long offset, i;
>> unsigned char *map;
>>
>> +if (!IS_ENABLED(CONFIG_THP_SWAP)) {
>> +VM_WARN_ON_ONCE(1);
>> +return 0;
>> +}
>
> I see you seized the opportunity to keep this code gloriously
> unencumbered by pesky comments. This seems like a time when you might
> have slipped up and been temped to add a comment or two. Guess not. :)
>
> Seriously, though, does it hurt us to add a comment or two to say
> something like:
>
> /*
>* Should not even be attempting cluster allocations when
>* huge page swap is disabled. Warn and fail the allocation.
>*/
> if (!IS_ENABLED(CONFIG_THP_SWAP)) {
> VM_WARN_ON_ONCE(1);
> return 0;
> }
I totally agree with you that we should add more comments for THP swap
to improve the code readability. As for this specific case,
VM_WARN_ON_ONCE() here is just to capture some programming error during
development. Do we really need comments here?
I will try to add more comments for other places in code regardless this
one.
Best Regards,
Huang, Ying
Re: [PATCH v2 2/7] mm/swapfile.c: Replace some #ifdef with IS_ENABLED()
> @@ -878,6 +877,11 @@ static int swap_alloc_cluster(struct swap_info_struct
> *si, swp_entry_t *slot)
> unsigned long offset, i;
> unsigned char *map;
>
> + if (!IS_ENABLED(CONFIG_THP_SWAP)) {
> + VM_WARN_ON_ONCE(1);
> + return 0;
> + }
I see you seized the opportunity to keep this code gloriously
unencumbered by pesky comments. This seems like a time when you might
have slipped up and been temped to add a comment or two. Guess not. :)
Seriously, though, does it hurt us to add a comment or two to say
something like:
/*
* Should not even be attempting cluster allocations when
* huge page swap is disabled. Warn and fail the allocation.
*/
if (!IS_ENABLED(CONFIG_THP_SWAP)) {
VM_WARN_ON_ONCE(1);
return 0;
}
Re: [PATCH v2 2/7] mm/swapfile.c: Replace some #ifdef with IS_ENABLED()
> @@ -878,6 +877,11 @@ static int swap_alloc_cluster(struct swap_info_struct
> *si, swp_entry_t *slot)
> unsigned long offset, i;
> unsigned char *map;
>
> + if (!IS_ENABLED(CONFIG_THP_SWAP)) {
> + VM_WARN_ON_ONCE(1);
> + return 0;
> + }
I see you seized the opportunity to keep this code gloriously
unencumbered by pesky comments. This seems like a time when you might
have slipped up and been temped to add a comment or two. Guess not. :)
Seriously, though, does it hurt us to add a comment or two to say
something like:
/*
* Should not even be attempting cluster allocations when
* huge page swap is disabled. Warn and fail the allocation.
*/
if (!IS_ENABLED(CONFIG_THP_SWAP)) {
VM_WARN_ON_ONCE(1);
return 0;
}
[PATCH v2 2/7] mm/swapfile.c: Replace some #ifdef with IS_ENABLED()
In mm/swapfile.c, THP (Transparent Huge Page) swap specific code is
enclosed by #ifdef CONFIG_THP_SWAP/#endif to avoid code dilating when
THP isn't enabled. But #ifdef/#endif in .c file hurt the code
readability, so Dave suggested to use IS_ENABLED(CONFIG_THP_SWAP)
instead and let compiler to do the dirty job for us. This has
potential to remove some duplicated code too. From output of `size`,
text data bss dec hex filename
THP=y: 26269 2076 340 28685700d mm/swapfile.o
ifdef/endif: 24115 2028 340 264836773 mm/swapfile.o
IS_ENABLED:24179 2028 340 2654767b3 mm/swapfile.o
IS_ENABLED() based solution works quite well, almost as good as that
of #ifdef/#endif. And from the diffstat, the removed lines are more
than added lines.
One #ifdef for split_swap_cluster() is kept. Because it is a public
function with a stub implementation for CONFIG_THP_SWAP=n in swap.h.
Signed-off-by: "Huang, Ying"
Suggested-by: Dave Hansen
Cc: Michal Hocko
Cc: Johannes Weiner
Cc: Shaohua Li
Cc: Hugh Dickins
Cc: Minchan Kim
Cc: Rik van Riel
Cc: Daniel Jordan
Cc: Dan Williams
---
mm/swapfile.c | 56
1 file changed, 16 insertions(+), 40 deletions(-)
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 0a2a9643dd78..dd9263411f11 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -870,7 +870,6 @@ static int scan_swap_map_slots(struct swap_info_struct *si,
return n_ret;
}
-#ifdef CONFIG_THP_SWAP
static int swap_alloc_cluster(struct swap_info_struct *si, swp_entry_t *slot)
{
unsigned long idx;
@@ -878,6 +877,11 @@ static int swap_alloc_cluster(struct swap_info_struct *si,
swp_entry_t *slot)
unsigned long offset, i;
unsigned char *map;
+ if (!IS_ENABLED(CONFIG_THP_SWAP)) {
+ VM_WARN_ON_ONCE(1);
+ return 0;
+ }
+
if (cluster_list_empty(>free_clusters))
return 0;
@@ -908,13 +912,6 @@ static void swap_free_cluster(struct swap_info_struct *si,
unsigned long idx)
unlock_cluster(ci);
swap_range_free(si, offset, SWAPFILE_CLUSTER);
}
-#else
-static int swap_alloc_cluster(struct swap_info_struct *si, swp_entry_t *slot)
-{
- VM_WARN_ON_ONCE(1);
- return 0;
-}
-#endif /* CONFIG_THP_SWAP */
static unsigned long scan_swap_map(struct swap_info_struct *si,
unsigned char usage)
@@ -1260,7 +1257,6 @@ static void swapcache_free(swp_entry_t entry)
}
}
-#ifdef CONFIG_THP_SWAP
static void swapcache_free_cluster(swp_entry_t entry)
{
unsigned long offset = swp_offset(entry);
@@ -1271,6 +1267,9 @@ static void swapcache_free_cluster(swp_entry_t entry)
unsigned int i, free_entries = 0;
unsigned char val;
+ if (!IS_ENABLED(CONFIG_THP_SWAP))
+ return;
+
si = _swap_info_get(entry);
if (!si)
return;
@@ -1306,6 +1305,7 @@ static void swapcache_free_cluster(swp_entry_t entry)
}
}
+#ifdef CONFIG_THP_SWAP
int split_swap_cluster(swp_entry_t entry)
{
struct swap_info_struct *si;
@@ -1320,11 +1320,7 @@ int split_swap_cluster(swp_entry_t entry)
unlock_cluster(ci);
return 0;
}
-#else
-static inline void swapcache_free_cluster(swp_entry_t entry)
-{
-}
-#endif /* CONFIG_THP_SWAP */
+#endif
void put_swap_page(struct page *page, swp_entry_t entry)
{
@@ -1483,7 +1479,6 @@ int swp_swapcount(swp_entry_t entry)
return count;
}
-#ifdef CONFIG_THP_SWAP
static bool swap_page_trans_huge_swapped(struct swap_info_struct *si,
swp_entry_t entry)
{
@@ -1494,6 +1489,9 @@ static bool swap_page_trans_huge_swapped(struct
swap_info_struct *si,
int i;
bool ret = false;
+ if (!IS_ENABLED(CONFIG_THP_SWAP))
+ return swap_swapcount(si, entry) != 0;
+
ci = lock_cluster_or_swap_info(si, offset);
if (!ci || !cluster_is_huge(ci)) {
if (map[roffset] != SWAP_HAS_CACHE)
@@ -1516,7 +1514,7 @@ static bool page_swapped(struct page *page)
swp_entry_t entry;
struct swap_info_struct *si;
- if (likely(!PageTransCompound(page)))
+ if (!IS_ENABLED(CONFIG_THP_SWAP) || likely(!PageTransCompound(page)))
return page_swapcount(page) != 0;
page = compound_head(page);
@@ -1540,10 +1538,8 @@ static int page_trans_huge_map_swapcount(struct page
*page, int *total_mapcount,
/* hugetlbfs shouldn't call it */
VM_BUG_ON_PAGE(PageHuge(page), page);
- if (likely(!PageTransCompound(page))) {
- mapcount = atomic_read(>_mapcount) + 1;
- if (total_mapcount)
- *total_mapcount = mapcount;
+ if (!IS_ENABLED(CONFIG_THP_SWAP) || likely(!PageTransCompound(page))) {
+ mapcount = page_trans_huge_mapcount(page,
[PATCH v2 2/7] mm/swapfile.c: Replace some #ifdef with IS_ENABLED()
In mm/swapfile.c, THP (Transparent Huge Page) swap specific code is
enclosed by #ifdef CONFIG_THP_SWAP/#endif to avoid code dilating when
THP isn't enabled. But #ifdef/#endif in .c file hurt the code
readability, so Dave suggested to use IS_ENABLED(CONFIG_THP_SWAP)
instead and let compiler to do the dirty job for us. This has
potential to remove some duplicated code too. From output of `size`,
text data bss dec hex filename
THP=y: 26269 2076 340 28685700d mm/swapfile.o
ifdef/endif: 24115 2028 340 264836773 mm/swapfile.o
IS_ENABLED:24179 2028 340 2654767b3 mm/swapfile.o
IS_ENABLED() based solution works quite well, almost as good as that
of #ifdef/#endif. And from the diffstat, the removed lines are more
than added lines.
One #ifdef for split_swap_cluster() is kept. Because it is a public
function with a stub implementation for CONFIG_THP_SWAP=n in swap.h.
Signed-off-by: "Huang, Ying"
Suggested-by: Dave Hansen
Cc: Michal Hocko
Cc: Johannes Weiner
Cc: Shaohua Li
Cc: Hugh Dickins
Cc: Minchan Kim
Cc: Rik van Riel
Cc: Daniel Jordan
Cc: Dan Williams
---
mm/swapfile.c | 56
1 file changed, 16 insertions(+), 40 deletions(-)
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 0a2a9643dd78..dd9263411f11 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -870,7 +870,6 @@ static int scan_swap_map_slots(struct swap_info_struct *si,
return n_ret;
}
-#ifdef CONFIG_THP_SWAP
static int swap_alloc_cluster(struct swap_info_struct *si, swp_entry_t *slot)
{
unsigned long idx;
@@ -878,6 +877,11 @@ static int swap_alloc_cluster(struct swap_info_struct *si,
swp_entry_t *slot)
unsigned long offset, i;
unsigned char *map;
+ if (!IS_ENABLED(CONFIG_THP_SWAP)) {
+ VM_WARN_ON_ONCE(1);
+ return 0;
+ }
+
if (cluster_list_empty(>free_clusters))
return 0;
@@ -908,13 +912,6 @@ static void swap_free_cluster(struct swap_info_struct *si,
unsigned long idx)
unlock_cluster(ci);
swap_range_free(si, offset, SWAPFILE_CLUSTER);
}
-#else
-static int swap_alloc_cluster(struct swap_info_struct *si, swp_entry_t *slot)
-{
- VM_WARN_ON_ONCE(1);
- return 0;
-}
-#endif /* CONFIG_THP_SWAP */
static unsigned long scan_swap_map(struct swap_info_struct *si,
unsigned char usage)
@@ -1260,7 +1257,6 @@ static void swapcache_free(swp_entry_t entry)
}
}
-#ifdef CONFIG_THP_SWAP
static void swapcache_free_cluster(swp_entry_t entry)
{
unsigned long offset = swp_offset(entry);
@@ -1271,6 +1267,9 @@ static void swapcache_free_cluster(swp_entry_t entry)
unsigned int i, free_entries = 0;
unsigned char val;
+ if (!IS_ENABLED(CONFIG_THP_SWAP))
+ return;
+
si = _swap_info_get(entry);
if (!si)
return;
@@ -1306,6 +1305,7 @@ static void swapcache_free_cluster(swp_entry_t entry)
}
}
+#ifdef CONFIG_THP_SWAP
int split_swap_cluster(swp_entry_t entry)
{
struct swap_info_struct *si;
@@ -1320,11 +1320,7 @@ int split_swap_cluster(swp_entry_t entry)
unlock_cluster(ci);
return 0;
}
-#else
-static inline void swapcache_free_cluster(swp_entry_t entry)
-{
-}
-#endif /* CONFIG_THP_SWAP */
+#endif
void put_swap_page(struct page *page, swp_entry_t entry)
{
@@ -1483,7 +1479,6 @@ int swp_swapcount(swp_entry_t entry)
return count;
}
-#ifdef CONFIG_THP_SWAP
static bool swap_page_trans_huge_swapped(struct swap_info_struct *si,
swp_entry_t entry)
{
@@ -1494,6 +1489,9 @@ static bool swap_page_trans_huge_swapped(struct
swap_info_struct *si,
int i;
bool ret = false;
+ if (!IS_ENABLED(CONFIG_THP_SWAP))
+ return swap_swapcount(si, entry) != 0;
+
ci = lock_cluster_or_swap_info(si, offset);
if (!ci || !cluster_is_huge(ci)) {
if (map[roffset] != SWAP_HAS_CACHE)
@@ -1516,7 +1514,7 @@ static bool page_swapped(struct page *page)
swp_entry_t entry;
struct swap_info_struct *si;
- if (likely(!PageTransCompound(page)))
+ if (!IS_ENABLED(CONFIG_THP_SWAP) || likely(!PageTransCompound(page)))
return page_swapcount(page) != 0;
page = compound_head(page);
@@ -1540,10 +1538,8 @@ static int page_trans_huge_map_swapcount(struct page
*page, int *total_mapcount,
/* hugetlbfs shouldn't call it */
VM_BUG_ON_PAGE(PageHuge(page), page);
- if (likely(!PageTransCompound(page))) {
- mapcount = atomic_read(>_mapcount) + 1;
- if (total_mapcount)
- *total_mapcount = mapcount;
+ if (!IS_ENABLED(CONFIG_THP_SWAP) || likely(!PageTransCompound(page))) {
+ mapcount = page_trans_huge_mapcount(page,
