* Re: [PATCH] mm: page_alloc: use the correct THP order for THP PCP
2024-04-03 13:47 [PATCH] mm: page_alloc: use the correct THP order for THP PCP Baolin Wang
@ 2024-04-04 10:03 ` Vlastimil Babka
2024-04-04 12:19 ` Baolin Wang
2024-04-04 14:00 ` Vlastimil Babka
2024-04-05 4:53 ` Barry Song
2 siblings, 1 reply; 7+ messages in thread
From: Vlastimil Babka @ 2024-04-04 10:03 UTC (permalink / raw)
To: Baolin Wang, akpm; +Cc: mgorman, linux-mm, linux-kernel
On 4/3/24 3:47 PM, Baolin Wang wrote:
> Commit 44042b449872 ("mm/page_alloc: allow high-order pages to be stored
> on the per-cpu lists") extends the PCP allocator to store THP pages, and
> it determines whether to cache THP pags in PCP by comparing with pageblock_order.
> But the pageblock_order is not always equal to THP order, it might also
> be MAX_PAGE_ORDER, which could prevent PCP from caching THP pages.
>
> Therefore, using HPAGE_PMD_ORDER instead to determine the need for caching
> THP for PCP can fix this issue
>
> Fixes: 44042b449872 ("mm/page_alloc: allow high-order pages to be stored on the per-cpu lists")
> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
IIUC this happens with CONFIG_HUGETLB_PAGE disabled because HUGETLBFS is
disabled? But THPs are still enabled? I think there might be more of THP
working suboptimally in that case with pageblock_order being larger
(MAX_PAGE_ORDER).
In other words, should be rather make pageblock_order itself defined as
min_t(unsigned int, HPAGE_PMD_ORDER, MAX_PAGE_ORDER)
in case with !CONFIG_HUGETLB_PAGE but THP enabled.
> ---
> mm/page_alloc.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 1beb56f75319..915f4ef070da 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -506,7 +506,7 @@ static inline unsigned int order_to_pindex(int migratetype, int order)
> {
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> if (order > PAGE_ALLOC_COSTLY_ORDER) {
> - VM_BUG_ON(order != pageblock_order);
> + VM_BUG_ON(order != HPAGE_PMD_ORDER);
> return NR_LOWORDER_PCP_LISTS;
> }
> #else
> @@ -522,7 +522,7 @@ static inline int pindex_to_order(unsigned int pindex)
>
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> if (pindex == NR_LOWORDER_PCP_LISTS)
> - order = pageblock_order;
> + order = HPAGE_PMD_ORDER;
> #else
> VM_BUG_ON(order > PAGE_ALLOC_COSTLY_ORDER);
> #endif
> @@ -535,7 +535,7 @@ static inline bool pcp_allowed_order(unsigned int order)
> if (order <= PAGE_ALLOC_COSTLY_ORDER)
> return true;
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> - if (order == pageblock_order)
> + if (order == HPAGE_PMD_ORDER)
> return true;
> #endif
> return false;
^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [PATCH] mm: page_alloc: use the correct THP order for THP PCP
2024-04-04 10:03 ` Vlastimil Babka
@ 2024-04-04 12:19 ` Baolin Wang
2024-04-04 14:01 ` Vlastimil Babka
0 siblings, 1 reply; 7+ messages in thread
From: Baolin Wang @ 2024-04-04 12:19 UTC (permalink / raw)
To: Vlastimil Babka, akpm; +Cc: mgorman, linux-mm, linux-kernel
On 2024/4/4 18:03, Vlastimil Babka wrote:
> On 4/3/24 3:47 PM, Baolin Wang wrote:
>> Commit 44042b449872 ("mm/page_alloc: allow high-order pages to be stored
>> on the per-cpu lists") extends the PCP allocator to store THP pages, and
>> it determines whether to cache THP pags in PCP by comparing with pageblock_order.
>> But the pageblock_order is not always equal to THP order, it might also
>> be MAX_PAGE_ORDER, which could prevent PCP from caching THP pages.
>>
>> Therefore, using HPAGE_PMD_ORDER instead to determine the need for caching
>> THP for PCP can fix this issue
>>
>> Fixes: 44042b449872 ("mm/page_alloc: allow high-order pages to be stored on the per-cpu lists")
>> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
>
> IIUC this happens with CONFIG_HUGETLB_PAGE disabled because HUGETLBFS is
> disabled? But THPs are still enabled? I think there might be more of THP
Right, and seems the Powerpc arch will set pageblock_order via
set_pageblock_order() when the huge page sizes are variable (not sure if
this is always equal to THP order).
Moreover, it still does not make sense to use pageblock_order to
indicate a THP page, especially when we already have HPAGE_PMD_ORDER to
represent THP.
> working suboptimally in that case with pageblock_order being larger
> (MAX_PAGE_ORDER).
>
> In other words, should be rather make pageblock_order itself defined as
>
> min_t(unsigned int, HPAGE_PMD_ORDER, MAX_PAGE_ORDER)
>
> in case with !CONFIG_HUGETLB_PAGE but THP enabled.
Yes, this makes sense to me (I wonder why this wasn't done before?). I
can create a seperate patch to do this, what do you think? Thanks.
^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [PATCH] mm: page_alloc: use the correct THP order for THP PCP
2024-04-04 12:19 ` Baolin Wang
@ 2024-04-04 14:01 ` Vlastimil Babka
0 siblings, 0 replies; 7+ messages in thread
From: Vlastimil Babka @ 2024-04-04 14:01 UTC (permalink / raw)
To: Baolin Wang, akpm; +Cc: mgorman, linux-mm, linux-kernel
On 4/4/24 2:19 PM, Baolin Wang wrote:
>
>
> On 2024/4/4 18:03, Vlastimil Babka wrote:
>> On 4/3/24 3:47 PM, Baolin Wang wrote:
>>> Commit 44042b449872 ("mm/page_alloc: allow high-order pages to be stored
>>> on the per-cpu lists") extends the PCP allocator to store THP pages, and
>>> it determines whether to cache THP pags in PCP by comparing with pageblock_order.
>>> But the pageblock_order is not always equal to THP order, it might also
>>> be MAX_PAGE_ORDER, which could prevent PCP from caching THP pages.
>>>
>>> Therefore, using HPAGE_PMD_ORDER instead to determine the need for caching
>>> THP for PCP can fix this issue
>>>
>>> Fixes: 44042b449872 ("mm/page_alloc: allow high-order pages to be stored on the per-cpu lists")
>>> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
>>
>> IIUC this happens with CONFIG_HUGETLB_PAGE disabled because HUGETLBFS is
>> disabled? But THPs are still enabled? I think there might be more of THP
>
> Right, and seems the Powerpc arch will set pageblock_order via
> set_pageblock_order() when the huge page sizes are variable (not sure if
> this is always equal to THP order).
>
> Moreover, it still does not make sense to use pageblock_order to
> indicate a THP page, especially when we already have HPAGE_PMD_ORDER to
> represent THP.
>
>> working suboptimally in that case with pageblock_order being larger
>> (MAX_PAGE_ORDER).
>>
>> In other words, should be rather make pageblock_order itself defined as
>>
>> min_t(unsigned int, HPAGE_PMD_ORDER, MAX_PAGE_ORDER)
>>
>> in case with !CONFIG_HUGETLB_PAGE but THP enabled.
>
> Yes, this makes sense to me (I wonder why this wasn't done before?). I
> can create a seperate patch to do this, what do you think? Thanks.
It probably wasn't anticipated that hugetlbfs would be disabled and THP
enabled. If you can create such patch, great!
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] mm: page_alloc: use the correct THP order for THP PCP
2024-04-03 13:47 [PATCH] mm: page_alloc: use the correct THP order for THP PCP Baolin Wang
2024-04-04 10:03 ` Vlastimil Babka
@ 2024-04-04 14:00 ` Vlastimil Babka
2024-04-05 4:53 ` Barry Song
2 siblings, 0 replies; 7+ messages in thread
From: Vlastimil Babka @ 2024-04-04 14:00 UTC (permalink / raw)
To: Baolin Wang, akpm; +Cc: mgorman, linux-mm, linux-kernel
On 4/3/24 3:47 PM, Baolin Wang wrote:
> Commit 44042b449872 ("mm/page_alloc: allow high-order pages to be stored
> on the per-cpu lists") extends the PCP allocator to store THP pages, and
> it determines whether to cache THP pags in PCP by comparing with pageblock_order.
> But the pageblock_order is not always equal to THP order, it might also
> be MAX_PAGE_ORDER, which could prevent PCP from caching THP pages.
>
> Therefore, using HPAGE_PMD_ORDER instead to determine the need for caching
> THP for PCP can fix this issue
>
> Fixes: 44042b449872 ("mm/page_alloc: allow high-order pages to be stored on the per-cpu lists")
> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
> ---
> mm/page_alloc.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 1beb56f75319..915f4ef070da 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -506,7 +506,7 @@ static inline unsigned int order_to_pindex(int migratetype, int order)
> {
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> if (order > PAGE_ALLOC_COSTLY_ORDER) {
> - VM_BUG_ON(order != pageblock_order);
> + VM_BUG_ON(order != HPAGE_PMD_ORDER);
> return NR_LOWORDER_PCP_LISTS;
> }
> #else
> @@ -522,7 +522,7 @@ static inline int pindex_to_order(unsigned int pindex)
>
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> if (pindex == NR_LOWORDER_PCP_LISTS)
> - order = pageblock_order;
> + order = HPAGE_PMD_ORDER;
> #else
> VM_BUG_ON(order > PAGE_ALLOC_COSTLY_ORDER);
> #endif
> @@ -535,7 +535,7 @@ static inline bool pcp_allowed_order(unsigned int order)
> if (order <= PAGE_ALLOC_COSTLY_ORDER)
> return true;
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> - if (order == pageblock_order)
> + if (order == HPAGE_PMD_ORDER)
> return true;
> #endif
> return false;
^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [PATCH] mm: page_alloc: use the correct THP order for THP PCP
2024-04-03 13:47 [PATCH] mm: page_alloc: use the correct THP order for THP PCP Baolin Wang
2024-04-04 10:03 ` Vlastimil Babka
2024-04-04 14:00 ` Vlastimil Babka
@ 2024-04-05 4:53 ` Barry Song
2024-04-05 12:16 ` Baolin Wang
2 siblings, 1 reply; 7+ messages in thread
From: Barry Song @ 2024-04-05 4:53 UTC (permalink / raw)
To: Baolin Wang; +Cc: akpm, mgorman, vbabka, linux-mm, linux-kernel
On Thu, Apr 4, 2024 at 2:47 AM Baolin Wang
<baolin.wang@linux.alibaba.com> wrote:
>
> Commit 44042b449872 ("mm/page_alloc: allow high-order pages to be stored
> on the per-cpu lists") extends the PCP allocator to store THP pages, and
> it determines whether to cache THP pags in PCP by comparing with pageblock_order.
> But the pageblock_order is not always equal to THP order, it might also
> be MAX_PAGE_ORDER, which could prevent PCP from caching THP pages.
>
> Therefore, using HPAGE_PMD_ORDER instead to determine the need for caching
> THP for PCP can fix this issue
>
> Fixes: 44042b449872 ("mm/page_alloc: allow high-order pages to be stored on the per-cpu lists")
> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
LGTM,
Reviewed-by: Barry Song <baohua@kernel.org>
In the context of using mTHP, perhaps there arises a need for PCP
allocation for frequently
requested mTHP orders. These orders typically exceed PAGE_ALLOC_COSTLY_ORDER
but are smaller than HPAGE_PMD_ORDER.
> ---
> mm/page_alloc.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 1beb56f75319..915f4ef070da 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -506,7 +506,7 @@ static inline unsigned int order_to_pindex(int migratetype, int order)
> {
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> if (order > PAGE_ALLOC_COSTLY_ORDER) {
> - VM_BUG_ON(order != pageblock_order);
> + VM_BUG_ON(order != HPAGE_PMD_ORDER);
> return NR_LOWORDER_PCP_LISTS;
> }
> #else
> @@ -522,7 +522,7 @@ static inline int pindex_to_order(unsigned int pindex)
>
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> if (pindex == NR_LOWORDER_PCP_LISTS)
> - order = pageblock_order;
> + order = HPAGE_PMD_ORDER;
> #else
> VM_BUG_ON(order > PAGE_ALLOC_COSTLY_ORDER);
> #endif
> @@ -535,7 +535,7 @@ static inline bool pcp_allowed_order(unsigned int order)
> if (order <= PAGE_ALLOC_COSTLY_ORDER)
> return true;
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> - if (order == pageblock_order)
> + if (order == HPAGE_PMD_ORDER)
> return true;
> #endif
> return false;
> --
> 2.39.3
>
Thanks
Barry
^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [PATCH] mm: page_alloc: use the correct THP order for THP PCP
2024-04-05 4:53 ` Barry Song
@ 2024-04-05 12:16 ` Baolin Wang
0 siblings, 0 replies; 7+ messages in thread
From: Baolin Wang @ 2024-04-05 12:16 UTC (permalink / raw)
To: Barry Song; +Cc: akpm, mgorman, vbabka, linux-mm, linux-kernel
On 2024/4/5 12:53, Barry Song wrote:
> On Thu, Apr 4, 2024 at 2:47 AM Baolin Wang
> <baolin.wang@linux.alibaba.com> wrote:
>>
>> Commit 44042b449872 ("mm/page_alloc: allow high-order pages to be stored
>> on the per-cpu lists") extends the PCP allocator to store THP pages, and
>> it determines whether to cache THP pags in PCP by comparing with pageblock_order.
>> But the pageblock_order is not always equal to THP order, it might also
>> be MAX_PAGE_ORDER, which could prevent PCP from caching THP pages.
>>
>> Therefore, using HPAGE_PMD_ORDER instead to determine the need for caching
>> THP for PCP can fix this issue
>>
>> Fixes: 44042b449872 ("mm/page_alloc: allow high-order pages to be stored on the per-cpu lists")
>> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
>
> LGTM,
> Reviewed-by: Barry Song <baohua@kernel.org>
>
> In the context of using mTHP, perhaps there arises a need for PCP
> allocation for frequently
> requested mTHP orders. These orders typically exceed PAGE_ALLOC_COSTLY_ORDER
> but are smaller than HPAGE_PMD_ORDER.
Yes, I have also considered this, but haven't found some time to do more
investigation and run some benchmarks.:) May be we can create a new
thread to talk about this first.
^ permalink raw reply [flat|nested] 7+ messages in thread