Re: [PATCH 09/10] mm/ksm: calc_checksum for folio

David Hildenbrand
2024-06-04T13:18:20Z

On 04.06.24 06:24, alexs@kernel.org wrote:
> From: "Alex Shi (tencent)" <alexs@kernel.org>
>
> Let's check the whole folio for contents change, don't count it if the
> folio changed.
>
> Signed-off-by: Alex Shi (tencent) <alexs@kernel.org>
> ---
> mm/ksm.c | 14 ++++++++------
> 1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/mm/ksm.c b/mm/ksm.c
> index b9c04ce677b9..dc2b5e6a9659 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -1258,11 +1258,13 @@ static int unmerge_and_remove_all_rmap_items(void)
> }
> #endif /* CONFIG_SYSFS */
>
> -static u32 calc_checksum(struct page *page)
> +static u32 calc_checksum(struct folio *folio)
> {
> u32 checksum;
> - void *addr = kmap_local_page(page);
> - checksum = xxhash(addr, PAGE_SIZE, 0);
> + int nr = folio_nr_pages(folio);
> + void *addr = kmap_local_page(folio_page(folio, 0));
> +
> + checksum = xxhash(addr, nr * PAGE_SIZE, 0);
> kunmap_local(addr);
> return checksum;
> }
> @@ -2369,7 +2371,7 @@ static void cmp_and_merge_page(struct page *page, struct ksm_rmap_item *rmap_ite
> * don't want to insert it in the unstable tree, and we don't want
> * to waste our time searching for something identical to it there.
> */
> - checksum = calc_checksum(page);
> + checksum = calc_checksum(folio);

So for a large folio you suddenly checksum more than a single page?
That's wrong.

Or am I missing something?

--
Cheers,

David / dhildenb