On 2024/8/19 17:28, Jonathan Cameron wrote:
> On Sat, 17 Aug 2024 16:49:37 +0800
> Kefeng Wang <wangkefeng.wang@xxxxxxxxxx> wrote:
>
>> Directly use a folio for HugeTLB and THP when calculate the next pfn,
>> then remove unused head variable.
>>
>> Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
>
> Hi,
>
> I was curious so had a read and have a quick comment
> on the comment.
>
>
>> ---
>> mm/memory_hotplug.c | 22 ++++++++++++++--------
>> 1 file changed, 14 insertions(+), 8 deletions(-)
>>
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index df291f2e509d..dc19b0e28fbc 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -1773,7 +1773,7 @@ static int scan_movable_pages(unsigned long start, unsigned long end,
>> static void do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
>> {
>> unsigned long pfn;
>> - struct page *page, *head;
>> + struct page *page;
>> LIST_HEAD(source);
>> static DEFINE_RATELIMIT_STATE(migrate_rs, DEFAULT_RATELIMIT_INTERVAL,
>> DEFAULT_RATELIMIT_BURST);
>> @@ -1786,14 +1786,20 @@ static void do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
>> continue;
>> page = pfn_to_page(pfn);
>> folio = page_folio(page);
>> - head = &folio->page;
>>
>> - if (PageHuge(page)) {
>> - pfn = page_to_pfn(head) + compound_nr(head) - 1;
>> - isolate_hugetlb(folio, &source);
>> - continue;
>> - } else if (PageTransHuge(page))
>> - pfn = page_to_pfn(head) + thp_nr_pages(page) - 1;
>> + /*
>> + * The folio hold no reference or lock, it might be changed
>> + * concurrently(eg, split), folio_nr_pages() may read garbage,
>> + * but out loop could handle that as it revisits the split
>> + * folio later.
>> + */
> Perhaps reword this (it confused me a bit) I'm not sure I've retained
> the intended meaning!
>
> * No reference or lock is held on the folio, so it might
> * be modified concurrently (e.g. split). As such,
> * folio_nr_pages() may read garbage. This is fine as the
> * outer loop will revisit the split folio later.
With above comment changed, this patch looks good to me.
Reviewed-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Thanks.
.
