Re: [PATCH v2 1/2] mm: use aligned address in clear_gigantic_page()

Huang, Ying
2024-10-28T06:20:57Z

Kefeng Wang <wangkefeng.wang@huawei.com> writes:

> When clearing gigantic page, it zeros page from the first page to the
> last page, if directly passing addr_hint which maybe not the address
> of the first page of folio, then some archs could flush the wrong cache
> if it does use the addr_hint as a hint. For non-gigantic page, it
> calculates the base address inside, even passed the wrong addr_hint, it
> only has performance impact as the process_huge_page() wants to process
> target page last to keep its cache lines hot), no functional impact.
>
> Let's pass the real accessed address to folio_zero_user() and use the
> aligned address in clear_gigantic_page() to fix it.
>
> Fixes: 78fefd04c123 ("mm: memory: convert clear_huge_page() to folio_zero_user()")
> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
> ---
> v2:
> - update changelog to clarify the impact, per Andrew
>
> fs/hugetlbfs/inode.c | 2 +-
> mm/memory.c | 1 +
> 2 files changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
> index a4441fb77f7c..a5ea006f403e 100644
> --- a/fs/hugetlbfs/inode.c
> +++ b/fs/hugetlbfs/inode.c
> @@ -825,7 +825,7 @@ static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset,
> error = PTR_ERR(folio);
> goto out;
> }
> - folio_zero_user(folio, ALIGN_DOWN(addr, hpage_size));
> + folio_zero_user(folio, addr);

'addr' is set with the following statement above,

/* addr is the offset within the file (zero based) */
addr = index * hpage_size;

So, we just don't need to ALIGN_DOWN() here. Or do I miss something?

> __folio_mark_uptodate(folio);
> error = hugetlb_add_to_page_cache(folio, mapping, index);
> if (unlikely(error)) {
> diff --git a/mm/memory.c b/mm/memory.c
> index 75c2dfd04f72..ef47b7ea5ddd 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -6821,6 +6821,7 @@ static void clear_gigantic_page(struct folio *folio, unsigned long addr,
> int i;
>
> might_sleep();
> + addr = ALIGN_DOWN(addr, folio_size(folio));
> for (i = 0; i < nr_pages; i++) {
> cond_resched();
> clear_user_highpage(folio_page(folio, i), addr + i * PAGE_SIZE);

--
Best Regards,
Huang, Ying