Re: [PATCH] CMA: Fix CMA's page number is substructed twice in __zone_watermark_ok
On Wed, Jan 7, 2015 at 4:45 PM, Vlastimil Babka wrote:
> On 12/30/2014 11:17 AM, Hui Zhu wrote:
>> The original of this patch [1] is used to fix the issue in Joonsoo's CMA
>> patch
>> "CMA: always treat free cma pages as non-free on watermark checking" [2].
>>
>> Joonsoo reminded me that this issue affect current kernel too. So made a new
>> one for upstream.
>>
>> Function __zone_watermark_ok substruct CMA pages number from free_pages
>> if system allocation can't use CMA areas:
>> /* If allocation can't use CMA areas don't use free CMA pages */
>> if (!(alloc_flags & ALLOC_CMA))
>> free_cma = zone_page_state(z, NR_FREE_CMA_PAGES);
>>
>> But after this part of code
>> for (o = 0; o < order; o++) {
>> /* At the next order, this order's pages become unavailable */
>> free_pages -= z->free_area[o].nr_free << o;
>> CMA memory in each order is part of z->free_area[o].nr_free, then the CMA
>> page number of this order is substructed twice. This bug will make
>> __zone_watermark_ok return more false.
>>
>> This patch add cma_free_area to struct free_area that just record the number
>> of CMA pages. And add it back in the order loop to handle the substruct
>> twice issue.
>
> Le sigh.
>
> I now dub CMA "Contagious Memory Allocator".
> One can't even take a Christmas vacation without this blight to spread :(
>
> Seriously, with so much special casing everywhere in fast paths, Minchan's
> (IIRC) proposal of a special CMA zone has some appeal.
>
> But it seems to me that the bug you are fixing doesn't exist as you describe
> it?
> free_cma is only used here:
>
> if (free_pages - free_cma <= min + z->lowmem_reserve[classzone_idx])
> return false;
>
> So it's subtracted from free_pages just temporarily for the basic order-0
> check.
> In the higher-order magic loop, it's not used at all?
>
I am so sorry that I made a mistake when I split this patch from the
patch series.
The original of this patch is to fix the issue around Joonsoo's update
of __zone_watermark_ok:
if (IS_ENABLED(CONFIG_CMA) && z->managed_cma_pages)
free_pages -= zone_page_state(z, NR_FREE_CMA_PAGES);
if (free_pages <= min + z->lowmem_reserve[classzone_idx])
return false;
Joonsoo, what about submit this change to upstream first?
Thanks,
Hui
> Vlastimil
>
>
>> [1] https://lkml.org/lkml/2014/12/25/43
>> [2] https://lkml.org/lkml/2014/5/28/110
>>
>> Signed-off-by: Hui Zhu
>> Signed-off-by: Weixing Liu
>> ---
>> include/linux/mmzone.h | 3 +++
>> mm/page_alloc.c| 22 ++
>> 2 files changed, 25 insertions(+)
>>
>> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
>> index 2f0856d..094476b 100644
>> --- a/include/linux/mmzone.h
>> +++ b/include/linux/mmzone.h
>> @@ -92,6 +92,9 @@ static inline int get_pfnblock_migratetype(struct page
>> *page, unsigned long pfn)
>> struct free_area {
>> struct list_headfree_list[MIGRATE_TYPES];
>> unsigned long nr_free;
>> +#ifdef CONFIG_CMA
>> + unsigned long cma_nr_free;
>> +#endif
>> };
>>
>> struct pglist_data;
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 7633c50..026cf27 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -650,6 +650,8 @@ static inline void __free_one_page(struct page *page,
>> } else {
>> list_del(&buddy->lru);
>> zone->free_area[order].nr_free--;
>> + if (is_migrate_cma(migratetype))
>> + zone->free_area[order].cma_nr_free--;
>> rmv_page_order(buddy);
>> }
>> combined_idx = buddy_idx & page_idx;
>> @@ -683,6 +685,8 @@ static inline void __free_one_page(struct page *page,
>> list_add(&page->lru, &zone->free_area[order].free_list[migratetype]);
>> out:
>> zone->free_area[order].nr_free++;
>> + if (is_migrate_cma(migratetype))
>> + zone->free_area[order].cma_nr_free++;
>> }
>>
>> static inline int free_pages_check(struct page *page)
>> @@ -937,6 +941,8 @@ static inline void expand(struct zone *zone, struct page
>> *page,
>> }
>> list_add(&page[size].lru, &area->free_list[migratetype]);
>> area->nr_free++;
>> + if (is_migrate_cma(migratetype))
>> + area->cma_nr_free++;
>> set_page_order(&page[size], high);
>> }
>> }
>> @@ -1020,6 +1026,8 @@ struct page *__rmqueue_smallest(struct zone *zone,
>> unsigned int order,
>> list_del(&page->lru);
>> rmv_page_order(page);
>> area->nr_free--;
>> + if (is_migrate_cma(migratetype))
>> + area->cma_nr_free--;
>> expand(zone, page, order, current_order, area, migratetype);
>> set_freepage_migratetype(page, migratetype);
>> return page;
>> @@ -1208,6 +1216,8 @@ __rmqueu
Re: [PATCH] CMA: Fix CMA's page number is substructed twice in __zone_watermark_ok
On 12/30/2014 11:17 AM, Hui Zhu wrote:
> The original of this patch [1] is used to fix the issue in Joonsoo's CMA patch
> "CMA: always treat free cma pages as non-free on watermark checking" [2].
>
> Joonsoo reminded me that this issue affect current kernel too. So made a new
> one for upstream.
>
> Function __zone_watermark_ok substruct CMA pages number from free_pages
> if system allocation can't use CMA areas:
> /* If allocation can't use CMA areas don't use free CMA pages */
> if (!(alloc_flags & ALLOC_CMA))
> free_cma = zone_page_state(z, NR_FREE_CMA_PAGES);
>
> But after this part of code
> for (o = 0; o < order; o++) {
> /* At the next order, this order's pages become unavailable */
> free_pages -= z->free_area[o].nr_free << o;
> CMA memory in each order is part of z->free_area[o].nr_free, then the CMA
> page number of this order is substructed twice. This bug will make
> __zone_watermark_ok return more false.
>
> This patch add cma_free_area to struct free_area that just record the number
> of CMA pages. And add it back in the order loop to handle the substruct
> twice issue.
Le sigh.
I now dub CMA "Contagious Memory Allocator".
One can't even take a Christmas vacation without this blight to spread :(
Seriously, with so much special casing everywhere in fast paths, Minchan's
(IIRC) proposal of a special CMA zone has some appeal.
But it seems to me that the bug you are fixing doesn't exist as you describe it?
free_cma is only used here:
if (free_pages - free_cma <= min + z->lowmem_reserve[classzone_idx])
return false;
So it's subtracted from free_pages just temporarily for the basic order-0 check.
In the higher-order magic loop, it's not used at all?
Vlastimil
> [1] https://lkml.org/lkml/2014/12/25/43
> [2] https://lkml.org/lkml/2014/5/28/110
>
> Signed-off-by: Hui Zhu
> Signed-off-by: Weixing Liu
> ---
> include/linux/mmzone.h | 3 +++
> mm/page_alloc.c| 22 ++
> 2 files changed, 25 insertions(+)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 2f0856d..094476b 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -92,6 +92,9 @@ static inline int get_pfnblock_migratetype(struct page
> *page, unsigned long pfn)
> struct free_area {
> struct list_headfree_list[MIGRATE_TYPES];
> unsigned long nr_free;
> +#ifdef CONFIG_CMA
> + unsigned long cma_nr_free;
> +#endif
> };
>
> struct pglist_data;
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 7633c50..026cf27 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -650,6 +650,8 @@ static inline void __free_one_page(struct page *page,
> } else {
> list_del(&buddy->lru);
> zone->free_area[order].nr_free--;
> + if (is_migrate_cma(migratetype))
> + zone->free_area[order].cma_nr_free--;
> rmv_page_order(buddy);
> }
> combined_idx = buddy_idx & page_idx;
> @@ -683,6 +685,8 @@ static inline void __free_one_page(struct page *page,
> list_add(&page->lru, &zone->free_area[order].free_list[migratetype]);
> out:
> zone->free_area[order].nr_free++;
> + if (is_migrate_cma(migratetype))
> + zone->free_area[order].cma_nr_free++;
> }
>
> static inline int free_pages_check(struct page *page)
> @@ -937,6 +941,8 @@ static inline void expand(struct zone *zone, struct page
> *page,
> }
> list_add(&page[size].lru, &area->free_list[migratetype]);
> area->nr_free++;
> + if (is_migrate_cma(migratetype))
> + area->cma_nr_free++;
> set_page_order(&page[size], high);
> }
> }
> @@ -1020,6 +1026,8 @@ struct page *__rmqueue_smallest(struct zone *zone,
> unsigned int order,
> list_del(&page->lru);
> rmv_page_order(page);
> area->nr_free--;
> + if (is_migrate_cma(migratetype))
> + area->cma_nr_free--;
> expand(zone, page, order, current_order, area, migratetype);
> set_freepage_migratetype(page, migratetype);
> return page;
> @@ -1208,6 +1216,8 @@ __rmqueue_fallback(struct zone *zone, unsigned int
> order, int start_migratetype)
> page = list_entry(area->free_list[migratetype].next,
> struct page, lru);
> area->nr_free--;
> + if (is_migrate_cma(migratetype))
> + area->cma_nr_free--;
>
> new_type = try_to_steal_freepages(zone, page,
> start_migratetype,
> @@ -1597,6 +1607,8 @@ int __isolate_free_page(struct page *page, unsigned int
> order)
> /*
Re: [PATCH] CMA: Fix CMA's page number is substructed twice in __zone_watermark_ok
Hello,
On Tue, Dec 30, 2014 at 06:17:25PM +0800, Hui Zhu wrote:
> The original of this patch [1] is used to fix the issue in Joonsoo's CMA patch
> "CMA: always treat free cma pages as non-free on watermark checking" [2].
>
> Joonsoo reminded me that this issue affect current kernel too. So made a new
> one for upstream.
>
> Function __zone_watermark_ok substruct CMA pages number from free_pages
> if system allocation can't use CMA areas:
> /* If allocation can't use CMA areas don't use free CMA pages */
> if (!(alloc_flags & ALLOC_CMA))
> free_cma = zone_page_state(z, NR_FREE_CMA_PAGES);
>
> But after this part of code
> for (o = 0; o < order; o++) {
> /* At the next order, this order's pages become unavailable */
> free_pages -= z->free_area[o].nr_free << o;
> CMA memory in each order is part of z->free_area[o].nr_free, then the CMA
> page number of this order is substructed twice. This bug will make
> __zone_watermark_ok return more false.
>
> This patch add cma_free_area to struct free_area that just record the number
> of CMA pages. And add it back in the order loop to handle the substruct
> twice issue.
>
> [1] https://lkml.org/lkml/2014/12/25/43
> [2] https://lkml.org/lkml/2014/5/28/110
>
> Signed-off-by: Hui Zhu
> Signed-off-by: Weixing Liu
> ---
> include/linux/mmzone.h | 3 +++
> mm/page_alloc.c| 22 ++
> 2 files changed, 25 insertions(+)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 2f0856d..094476b 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -92,6 +92,9 @@ static inline int get_pfnblock_migratetype(struct page
> *page, unsigned long pfn)
> struct free_area {
> struct list_headfree_list[MIGRATE_TYPES];
> unsigned long nr_free;
> +#ifdef CONFIG_CMA
> + unsigned long cma_nr_free;
> +#endif
> };
>
> struct pglist_data;
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 7633c50..026cf27 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -650,6 +650,8 @@ static inline void __free_one_page(struct page *page,
> } else {
> list_del(&buddy->lru);
> zone->free_area[order].nr_free--;
> + if (is_migrate_cma(migratetype))
> + zone->free_area[order].cma_nr_free--;
cma_nr_free is defined only if CONFIG_CMA. If !CONFIG_CMA, this would
cause build failure. How about making new function to manipulate
nr_free, cma_nr_free and use it on each sites?
And, if pageblock for CMA is isolated, cma_nr_free would be
miscalculated. Think about following situation.
One freepage (A) in CMA.
zone->free_area[0].nr_free = 1
zone->free_area[0].cma_nr_free = 1
zone->free_area[1].nr_free = 0
zone->free_area[1].cma_nr_free = 0
Isolate the pageblock having (A)
__free_one_page() with buddy page of (A)
Intermediate state of free_area after above logic
zone->free_area[0].nr_free = 0
zone->free_area[0].cma_nr_free = 1
zone->free_area[1].nr_free = 0
zone->free_area[1].cma_nr_free = 0
Final state of free_area after merging
zone->free_area[0].nr_free = 0
zone->free_area[0].cma_nr_free = 1
zone->free_area[1].nr_free = 1
zone->free_area[1].cma_nr_free = 0
> rmv_page_order(buddy);
> }
> combined_idx = buddy_idx & page_idx;
> @@ -683,6 +685,8 @@ static inline void __free_one_page(struct page *page,
> list_add(&page->lru, &zone->free_area[order].free_list[migratetype]);
> out:
> zone->free_area[order].nr_free++;
> + if (is_migrate_cma(migratetype))
> + zone->free_area[order].cma_nr_free++;
> }
>
> static inline int free_pages_check(struct page *page)
> @@ -937,6 +941,8 @@ static inline void expand(struct zone *zone, struct page
> *page,
> }
> list_add(&page[size].lru, &area->free_list[migratetype]);
> area->nr_free++;
> + if (is_migrate_cma(migratetype))
> + area->cma_nr_free++;
> set_page_order(&page[size], high);
> }
> }
> @@ -1020,6 +1026,8 @@ struct page *__rmqueue_smallest(struct zone *zone,
> unsigned int order,
> list_del(&page->lru);
> rmv_page_order(page);
> area->nr_free--;
> + if (is_migrate_cma(migratetype))
> + area->cma_nr_free--;
> expand(zone, page, order, current_order, area, migratetype);
> set_freepage_migratetype(page, migratetype);
> return page;
> @@ -1208,6 +1216,8 @@ __rmqueue_fallback(struct zone *zone, unsigned int
> order, int start_migratetype)
> page = list_entry(area->free_list[migratetype].next,
> struct page, lru);
> area->nr_free--;
> + if (is_migrate_cma(migratetype))
> +
[PATCH] CMA: Fix CMA's page number is substructed twice in __zone_watermark_ok
The original of this patch [1] is used to fix the issue in Joonsoo's CMA patch
"CMA: always treat free cma pages as non-free on watermark checking" [2].
Joonsoo reminded me that this issue affect current kernel too. So made a new
one for upstream.
Function __zone_watermark_ok substruct CMA pages number from free_pages
if system allocation can't use CMA areas:
/* If allocation can't use CMA areas don't use free CMA pages */
if (!(alloc_flags & ALLOC_CMA))
free_cma = zone_page_state(z, NR_FREE_CMA_PAGES);
But after this part of code
for (o = 0; o < order; o++) {
/* At the next order, this order's pages become unavailable */
free_pages -= z->free_area[o].nr_free << o;
CMA memory in each order is part of z->free_area[o].nr_free, then the CMA
page number of this order is substructed twice. This bug will make
__zone_watermark_ok return more false.
This patch add cma_free_area to struct free_area that just record the number
of CMA pages. And add it back in the order loop to handle the substruct
twice issue.
[1] https://lkml.org/lkml/2014/12/25/43
[2] https://lkml.org/lkml/2014/5/28/110
Signed-off-by: Hui Zhu
Signed-off-by: Weixing Liu
---
include/linux/mmzone.h | 3 +++
mm/page_alloc.c| 22 ++
2 files changed, 25 insertions(+)
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 2f0856d..094476b 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -92,6 +92,9 @@ static inline int get_pfnblock_migratetype(struct page *page,
unsigned long pfn)
struct free_area {
struct list_headfree_list[MIGRATE_TYPES];
unsigned long nr_free;
+#ifdef CONFIG_CMA
+ unsigned long cma_nr_free;
+#endif
};
struct pglist_data;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 7633c50..026cf27 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -650,6 +650,8 @@ static inline void __free_one_page(struct page *page,
} else {
list_del(&buddy->lru);
zone->free_area[order].nr_free--;
+ if (is_migrate_cma(migratetype))
+ zone->free_area[order].cma_nr_free--;
rmv_page_order(buddy);
}
combined_idx = buddy_idx & page_idx;
@@ -683,6 +685,8 @@ static inline void __free_one_page(struct page *page,
list_add(&page->lru, &zone->free_area[order].free_list[migratetype]);
out:
zone->free_area[order].nr_free++;
+ if (is_migrate_cma(migratetype))
+ zone->free_area[order].cma_nr_free++;
}
static inline int free_pages_check(struct page *page)
@@ -937,6 +941,8 @@ static inline void expand(struct zone *zone, struct page
*page,
}
list_add(&page[size].lru, &area->free_list[migratetype]);
area->nr_free++;
+ if (is_migrate_cma(migratetype))
+ area->cma_nr_free++;
set_page_order(&page[size], high);
}
}
@@ -1020,6 +1026,8 @@ struct page *__rmqueue_smallest(struct zone *zone,
unsigned int order,
list_del(&page->lru);
rmv_page_order(page);
area->nr_free--;
+ if (is_migrate_cma(migratetype))
+ area->cma_nr_free--;
expand(zone, page, order, current_order, area, migratetype);
set_freepage_migratetype(page, migratetype);
return page;
@@ -1208,6 +1216,8 @@ __rmqueue_fallback(struct zone *zone, unsigned int order,
int start_migratetype)
page = list_entry(area->free_list[migratetype].next,
struct page, lru);
area->nr_free--;
+ if (is_migrate_cma(migratetype))
+ area->cma_nr_free--;
new_type = try_to_steal_freepages(zone, page,
start_migratetype,
@@ -1597,6 +1607,8 @@ int __isolate_free_page(struct page *page, unsigned int
order)
/* Remove page from free list */
list_del(&page->lru);
zone->free_area[order].nr_free--;
+ if (is_migrate_cma(mt))
+ zone->free_area[order].cma_nr_free--;
rmv_page_order(page);
/* Set the pageblock if the isolated page is at least a pageblock */
@@ -1827,6 +1839,13 @@ static bool __zone_watermark_ok(struct zone *z, unsigned
int order,
/* At the next order, this order's pages become unavailable */
free_pages -= z->free_area[o].nr_free << o;
+ /* If CMA's page number of this order was substructed as part
+ of "zone_page_state(z, NR_FREE_CMA_PAGES)", subtracting
+ "z->free_area[o].nr_free << o" substructed CMA's page
+ number of
