Re: [PATCH v5] mm/page_owner.c: add llseek for page_owner

[Kassey Li <quic_yingangl@quicinc.com>]

On 8/9/2022 5:30 PM, Vlastimil Babka (SUSE) wrote:
> On 8/9/22 04:47, Kassey Li wrote:
>> There is usage to dump a given cma region page_owner
>> instead of all page's.
>>
>> This change allows to specify a ppos as start_pfn
>> by fseek.
>>
>> Any invalid ppos will be skipped, so it did not
>> broken the origin dump feature.
>>
>> Suggested-by: Vlastimil Babka <vbabka@suse.cz>
>> Signed-off-by: Kassey Li <quic_yingangl@quicinc.com>
>> ---
>>   Documentation/vm/page_owner.rst | 6 ++++++
>>   mm/internal.h                   | 5 +++++
>>   mm/page_owner.c                 | 9 ++++++---
>>   3 files changed, 17 insertions(+), 3 deletions(-)
>>
>> diff --git a/Documentation/vm/page_owner.rst b/Documentation/vm/page_owner.rst
>> index f5c954afe97c..8d33d976da8a 100644
>> --- a/Documentation/vm/page_owner.rst
>> +++ b/Documentation/vm/page_owner.rst
>> @@ -95,6 +95,12 @@ Usage
>>   	PFN XXX ...
>>   	// Detailed stack
>>   
>> +   By default, it will do full pfn dump, to start with a given pfn,
>> +   page_owner supports fseek.
>> +
>> +   FILE *fp = fopen("/sys/kernel/debug/page_owner", "r");
>> +   fseek(fp, pfn_start, SEEK_SET);
>> +
>>      The ``page_owner_sort`` tool ignores ``PFN`` rows, puts the remaining rows
>>      in buf, uses regexp to extract the page order value, counts the times
>>      and pages of buf, and finally sorts them according to the parameter(s).
>> diff --git a/mm/internal.h b/mm/internal.h
>> index c0f8fbe0445b..1ad8f86e6e33 100644
>> --- a/mm/internal.h
>> +++ b/mm/internal.h
>> @@ -189,6 +189,11 @@ extern void reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason
>>    */
>>   extern pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address);
>>   
>> +/*
>> + * in mm/page_owner.c:
> 
> This should say where it's defined, not used from, and that's
> fs/proc/base.c. But it's already declared in fs/proc/internal.h so maybe
> page_owner.c could just include that header (although it's a bit meh).
ok, let's do it.
> 
>> + */
>> +extern loff_t mem_lseek(struct file *, loff_t, int);
>> +
>>   /*
>>    * in mm/page_alloc.c
>>    */
>> diff --git a/mm/page_owner.c b/mm/page_owner.c
>> index e4c6f3f1695b..dcbe05e206e1 100644
>> --- a/mm/page_owner.c
>> +++ b/mm/page_owner.c
>> @@ -497,8 +497,10 @@ read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos)
>>   		return -EINVAL;
>>   
>>   	page = NULL;
>> -	pfn = min_low_pfn + *ppos;
>> -
>> +	if (*ppos == 0)
>> +		pfn= min_low_pfn;
> 
> missing space before '='

   my bad, for v6

./scripts/checkpatch.pl 
v6-0001-mm-page_owner.c-add-llseek-for-page_owner.patch
total: 0 errors, 0 warnings, 46 lines checked

v6-0001-mm-page_owner.c-add-llseek-for-page_owner.patch has no obvious 
style problems and is ready for submission.
> 
>> +	else
>> +		pfn = *ppos;
>>   	/* Find a valid PFN or the start of a MAX_ORDER_NR_PAGES area */
>>   	while (!pfn_valid(pfn) && (pfn & (MAX_ORDER_NR_PAGES - 1)) != 0)
>>   		pfn++;
>> @@ -561,7 +563,7 @@ read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos)
>>   			continue;
>>   
>>   		/* Record the next PFN to read in the file offset */
>> -		*ppos = (pfn - min_low_pfn) + 1;
>> +		*ppos = pfn + 1;
>>   
>>   		return print_page_owner(buf, count, pfn, page,
>>   				page_owner, handle);
>> @@ -660,6 +662,7 @@ static void init_early_allocated_pages(void)
>>   
>>   static const struct file_operations proc_page_owner_operations = {
>>   	.read		= read_page_owner,
>> +	.llseek 	= mem_lseek,
>>   };
>>   
>>   static int __init pageowner_init(void)
>