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SubjectRe: [PATCH v4] mm/page_owner.c: add llseek for page_owner
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On 8/8/2022 11:33 PM, Vlastimil Babka (SUSE) wrote:
> On 8/8/22 09:36, 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 (SUSE) <vbabka@kernel.org>
>
> Thanks, but please change it to Vlastimil Babka <vbabka@suse.cz>
> It was some mistake between me and thunderbird that it was sent from @k.o.
Ok, will change it.
>
>> Signed-off-by: Kassey Li <quic_yingangl@quicinc.com>
>> ---
>> mm/page_owner.c | 20 ++++++++++++++++++--
>> 1 file changed, 18 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/page_owner.c b/mm/page_owner.c
>> index e4c6f3f1695b..231b1877af99 100644
>> --- a/mm/page_owner.c
>> +++ b/mm/page_owner.c
>> @@ -497,8 +497,8 @@ read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos)
>> return -EINVAL;
>>
>> page = NULL;
>> - pfn = min_low_pfn + *ppos;
>>
>> + pfn = *ppos;
>
> Maybe we could still optimize the typical case a bit such that when it's 0,
> we skip to min_low_pfn immediately.
>
>> /* 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 +561,7 @@ 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);
>> @@ -570,6 +570,21 @@ read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos)
>> return 0;
>> }
>>
>> +static loff_t llseek_page_owner(struct file *file, loff_t offset, int whence)
>> +{
>> + loff_t retval = 0;
>> + switch (whence) {
>> + case SEEK_CUR:
>
> It's not correct for SEEK_CUR to behave like this, no?
> Can we perhaps reuse the existing mem_lseek() ?
agree.
>
> Also we should update Documentation/mm/page_owner.rst to document the lseek
> support and that it works with a pfn.
will do this in v5 patch set.
>
> Thanks!
>
>> + case SEEK_SET:
>> + file->f_pos = offset;
>> + break;
>> + default:
>> + retval = -ENXIO;
>> + }
>> +
>> + return retval;
>> +}
>> +
>> static void init_pages_in_zone(pg_data_t *pgdat, struct zone *zone)
>> {
>> unsigned long pfn = zone->zone_start_pfn;
>> @@ -660,6 +675,7 @@ static void init_early_allocated_pages(void)
>>
>> static const struct file_operations proc_page_owner_operations = {
>> .read = read_page_owner,
>> + .llseek = llseek_page_owner,
>> };
>>
>> static int __init pageowner_init(void)
>

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