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Message-ID: <dfbced2e-487c-413f-bfed-567a852ab1bc@gmail.com>
Date: Thu, 25 Apr 2024 01:58:53 +0800
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Subject: Re: [PATCH 1/2] mm: add per-order mTHP split counters
From: Bang Li <libang.linux@gmail.com>
To: Lance Yang <ioworker0@gmail.com>
Cc: akpm@linux-foundation.org, 21cnbao@gmail.com, ryan.roberts@arm.com,
 david@redhat.com, baolin.wang@linux.alibaba.com,
 linux-kernel@vger.kernel.org, linux-mm@kvack.org,
 Bang Li <libang.linux@gmail.com>
References: <20240424135148.30422-1-ioworker0@gmail.com>
 <20240424135148.30422-2-ioworker0@gmail.com>
 <1192295a-5b94-4c1a-b11c-7cd8ef0e62b7@gmail.com>
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Hey, sorry for making noise, there was something wrong with the format of
the last email.

On 2024/4/25 1:12, Bang Li wrote:
> Hey Lance,
>
> On 2024/4/24 21:51, Lance Yang wrote:
>
>> At present, the split counters in THP statistics no longer include
>> PTE-mapped mTHP. Therefore, this commit introduces per-order mTHP split
>> counters to monitor the frequency of mTHP splits. This will assist
>> developers in better analyzing and optimizing system performance.
>>
>> /sys/kernel/mm/transparent_hugepage/hugepages-<size>/stats
>>          split_page
>>          split_page_failed
>>          deferred_split_page
>>
>> Signed-off-by: Lance Yang <ioworker0@gmail.com>
>> ---
>>   include/linux/huge_mm.h |  3 +++
>>   mm/huge_memory.c        | 14 ++++++++++++--
>>   2 files changed, 15 insertions(+), 2 deletions(-)
>>
>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
>> index 56c7ea73090b..7b9c6590e1f7 100644
>> --- a/include/linux/huge_mm.h
>> +++ b/include/linux/huge_mm.h
>> @@ -272,6 +272,9 @@ enum mthp_stat_item {
>>       MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE,
>>       MTHP_STAT_ANON_SWPOUT,
>>       MTHP_STAT_ANON_SWPOUT_FALLBACK,
>> +    MTHP_STAT_SPLIT_PAGE,
>> +    MTHP_STAT_SPLIT_PAGE_FAILED,
>> +    MTHP_STAT_DEFERRED_SPLIT_PAGE,
>>       __MTHP_STAT_COUNT
>>   };
>>   diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> index 055df5aac7c3..52db888e47a6 100644
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>> @@ -557,6 +557,9 @@ DEFINE_MTHP_STAT_ATTR(anon_fault_fallback, 
>> MTHP_STAT_ANON_FAULT_FALLBACK);
>>   DEFINE_MTHP_STAT_ATTR(anon_fault_fallback_charge, 
>> MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE);
>>   DEFINE_MTHP_STAT_ATTR(anon_swpout, MTHP_STAT_ANON_SWPOUT);
>>   DEFINE_MTHP_STAT_ATTR(anon_swpout_fallback, 
>> MTHP_STAT_ANON_SWPOUT_FALLBACK);
>> +DEFINE_MTHP_STAT_ATTR(split_page, MTHP_STAT_SPLIT_PAGE);
>> +DEFINE_MTHP_STAT_ATTR(split_page_failed, MTHP_STAT_SPLIT_PAGE_FAILED);
>> +DEFINE_MTHP_STAT_ATTR(deferred_split_page, 
>> MTHP_STAT_DEFERRED_SPLIT_PAGE);
>>     static struct attribute *stats_attrs[] = {
>>       &anon_fault_alloc_attr.attr,
>> @@ -564,6 +567,9 @@ static struct attribute *stats_attrs[] = {
>>       &anon_fault_fallback_charge_attr.attr,
>>       &anon_swpout_attr.attr,
>>       &anon_swpout_fallback_attr.attr,
>> +    &split_page_attr.attr,
>> +    &split_page_failed_attr.attr,
>> +    &deferred_split_page_attr.attr,
>>       NULL,
>>   };
>>   @@ -3083,7 +3089,7 @@ int split_huge_page_to_list_to_order(struct 
>> page *page, struct list_head *list,
>>       XA_STATE_ORDER(xas, &folio->mapping->i_pages, folio->index, 
>> new_order);
>>       struct anon_vma *anon_vma = NULL;
>>       struct address_space *mapping = NULL;
>> -    bool is_thp = folio_test_pmd_mappable(folio);
>> +    int order = folio_order(folio);
>>       int extra_pins, ret;
>>       pgoff_t end;
>>       bool is_hzp;
>> @@ -3262,8 +3268,10 @@ int split_huge_page_to_list_to_order(struct 
>> page *page, struct list_head *list,
>>           i_mmap_unlock_read(mapping);
>>   out:
>>       xas_destroy(&xas);
>> -    if (is_thp)
>> +    if (order >= HPAGE_PMD_ORDER)
>>           count_vm_event(!ret ? THP_SPLIT_PAGE : THP_SPLIT_PAGE_FAILED);
>> +    count_mthp_stat(order, !ret ? MTHP_STAT_SPLIT_PAGE :
>> +                      MTHP_STAT_SPLIT_PAGE_FAILED);
>>       return ret;
>>   }
>>   @@ -3327,6 +3335,8 @@ void deferred_split_folio(struct folio *folio)
>>       if (list_empty(&folio->_deferred_list)) {
>>           if (folio_test_pmd_mappable(folio))
>>               count_vm_event(THP_DEFERRED_SPLIT_PAGE);
>> +        count_mthp_stat(folio_order(folio),
>> +                MTHP_STAT_DEFERRED_SPLIT_PAGE);
>>           list_add_tail(&folio->_deferred_list, &ds_queue->split_queue);
>>           ds_queue->split_queue_len++;
>>   #ifdef CONFIG_MEMCG
>
> My opinion can be ignored :). Would it be better to modify the 
> deferred_split_folio
> function as follows? I'm not sure.
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 
> 055df5aac7c3..e8562e8630b1 100644 --- a/mm/huge_memory.c +++ 
> b/mm/huge_memory.c @@ -3299,12 +3299,13 @@ void 
> deferred_split_folio(struct folio *folio) struct mem_cgroup *memcg = 
> folio_memcg(folio); #endif unsigned long flags; + int order = 
> folio_order(folio); /* * Order 1 folios have no space for a deferred 
> list, but we also * won't waste much memory by not adding them to the 
> deferred list. */ - if (folio_order(folio) <= 1) + if (order <= 1) 
> return; /* @@ -3325,8 +3326,9 @@ void deferred_split_folio(struct 
> folio *folio) spin_lock_irqsave(&ds_queue->split_queue_lock, flags); 
> if (list_empty(&folio->_deferred_list)) { - if 
> (folio_test_pmd_mappable(folio)) + if (order >= HPAGE_PMD_ORDER) 
> count_vm_event(THP_DEFERRED_SPLIT_PAGE); + count_mthp_stat(order, 
> MTHP_STAT_DEFERRED_SPLIT_PAGE); list_add_tail(&folio->_deferred_list, 
> &ds_queue->split_queue); ds_queue->split_queue_len++; #ifdef 
> CONFIG_MEMCG thanks,
> bang
>

My opinion can be ignored :). Would it be better to modify the 
deferred_split_folio
function as follows? I'm not sure.

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 055df5aac7c3..e8562e8630b1 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3299,12 +3299,13 @@ void deferred_split_folio(struct folio *folio)
         struct mem_cgroup *memcg = folio_memcg(folio);
  #endif
         unsigned long flags;
+       int order = folio_order(folio);

         /*
          * Order 1 folios have no space for a deferred list, but we also
          * won't waste much memory by not adding them to the deferred list.
          */
-       if (folio_order(folio) <= 1)
+       if (order <= 1)
                 return;

         /*
@@ -3325,8 +3326,9 @@ void deferred_split_folio(struct folio *folio)

         spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
         if (list_empty(&folio->_deferred_list)) {
-               if (folio_test_pmd_mappable(folio))
+               if (order >= HPAGE_PMD_ORDER)
                         count_vm_event(THP_DEFERRED_SPLIT_PAGE);
+               count_mthp_stat(order, MTHP_STAT_DEFERRED_SPLIT_PAGE);
                 list_add_tail(&folio->_deferred_list, 
&ds_queue->split_queue);
                 ds_queue->split_queue_len++;
  #ifdef CONFIG_MEMCG

thanks,
bang