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.
> + if (folio_test_large(folio)) {
> + pfn = folio_pfn(folio) + folio_nr_pages(folio) - 1;
> + if (folio_test_hugetlb(folio)) {
> + isolate_hugetlb(folio, &source);
> + continue;
> + }
> + }
>
> /*
> * HWPoison pages have elevated reference counts so the migration would
