Re: [PATCH] mm/shmem: add mTHP swpout fallback statistics in shmem_writeout()

[Weilin Tong <tongweilin@linux.alibaba.com>]

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在 2025/12/16 14:34, Anshuman Khandual 写道:
>
> On 15/12/25 8:16 AM, Weilin Tong wrote:
>> Currently, when shmem mTHPs are split and swapped out via shmem_writeout(),
>> there are no unified statistics to trace these mTHP swpout fallback events.
>> This makes it difficult to analyze the prevalence of mTHP splitting and
>> fallback during swap operations, which is important for memory diagnostics.
>>
>> Here we add statistics counting for mTHP fallback to small pages
>> when splitting and swapping out in shmem_writeout().
>>
>> Signed-off-by: Weilin Tong<tongweilin@linux.alibaba.com>
>> Reviewed-by: Baolin Wang<baolin.wang@linux.alibaba.com>
>> ---
>>   mm/shmem.c | 12 ++++++++++++
>>   1 file changed, 12 insertions(+)
>>
>> diff --git a/mm/shmem.c b/mm/shmem.c
>> index 3f194c9842a8..aa624c447358 100644
>> --- a/mm/shmem.c
>> +++ b/mm/shmem.c
>> @@ -1593,11 +1593,23 @@ int shmem_writeout(struct folio *folio, struct swap_iocb **plug,
>>   	}
>>   
>>   	if (split) {
>> +		int order;
>> +
> Could this be moved up near the 'nr_pages' declaration instead ?

Thanks for your reviewing.

IIUC, this|order|variable is only used inside the|"if (split)"|code block, so it's best to define it here. This keeps its scope limited.

>>   try_split:
>> +		order = folio_order(folio);
>>   		/* Ensure the subpages are still dirty */
>>   		folio_test_set_dirty(folio);
>>   		if (split_folio_to_list(folio, folio_list))
>>   			goto redirty;
>> +
>> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>> +		if (order >= HPAGE_PMD_ORDER) {
>> +			count_memcg_folio_events(folio, THP_SWPOUT_FALLBACK, 1);
>> +			count_vm_event(THP_SWPOUT_FALLBACK);
>> +		}
>> +#endif
>> +		count_mthp_stat(order, MTHP_STAT_SWPOUT_FALLBACK);
>> +
>>   		folio_clear_dirty(folio);
>>   	}
>>   
> Otherwise LGTM.

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