Re: [PATCH v13 2/7] mm: factor helpers for memory_failure_dev_pagemap

HORIGUCHI NAOYA(堀口 直也)
2022-04-21T06:13:52Z

On Tue, Apr 19, 2022 at 12:50:40PM +0800, Shiyang Ruan wrote:
> memory_failure_dev_pagemap code is a bit complex before introduce RMAP
> feature for fsdax. So it is needed to factor some helper functions to
> simplify these code.
>
> Signed-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com>
> Reviewed-by: Darrick J. Wong <djwong@kernel.org>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Dan Williams <dan.j.williams@intel.com>

Thanks for the refactoring. As I commented to 0/7, the conflict with
"mm/hwpoison: fix race between hugetlb free/demotion and memory_failure_hugetlb()"
can be trivially resolved.

Another few comment below ...

> ---
> mm/memory-failure.c | 157 ++++++++++++++++++++++++--------------------
> 1 file changed, 87 insertions(+), 70 deletions(-)
>
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index e3fbff5bd467..7c8c047bfdc8 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1498,6 +1498,90 @@ static int try_to_split_thp_page(struct page *page, const char *msg)
> return 0;
> }
>
> +static void unmap_and_kill(struct list_head *to_kill, unsigned long pfn,
> + struct address_space *mapping, pgoff_t index, int flags)
> +{
> + struct to_kill *tk;
> + unsigned long size = 0;
> +
> + list_for_each_entry(tk, to_kill, nd)
> + if (tk->size_shift)
> + size = max(size, 1UL << tk->size_shift);
> +
> + if (size) {
> + /*
> + * Unmap the largest mapping to avoid breaking up device-dax
> + * mappings which are constant size. The actual size of the
> + * mapping being torn down is communicated in siginfo, see
> + * kill_proc()
> + */
> + loff_t start = (index << PAGE_SHIFT) & ~(size - 1);
> +
> + unmap_mapping_range(mapping, start, size, 0);
> + }
> +
> + kill_procs(to_kill, flags & MF_MUST_KILL, false, pfn, flags);
> +}
> +
> +static int mf_generic_kill_procs(unsigned long long pfn, int flags,
> + struct dev_pagemap *pgmap)
> +{
> + struct page *page = pfn_to_page(pfn);
> + LIST_HEAD(to_kill);
> + dax_entry_t cookie;
> + int rc = 0;
> +
> + /*
> + * Pages instantiated by device-dax (not filesystem-dax)
> + * may be compound pages.
> + */
> + page = compound_head(page);
> +
> + /*
> + * Prevent the inode from being freed while we are interrogating
> + * the address_space, typically this would be handled by
> + * lock_page(), but dax pages do not use the page lock. This
> + * also prevents changes to the mapping of this pfn until
> + * poison signaling is complete.
> + */
> + cookie = dax_lock_page(page);
> + if (!cookie)
> + return -EBUSY;
> +
> + if (hwpoison_filter(page)) {
> + rc = -EOPNOTSUPP;
> + goto unlock;
> + }
> +
> + if (pgmap->type == MEMORY_DEVICE_PRIVATE) {
> + /*
> + * TODO: Handle HMM pages which may need coordination
> + * with device-side memory.
> + */
> + return -EBUSY;

Don't we need to go to dax_unlock_page() as the origincal code do?

> + }
> +
> + /*
> + * Use this flag as an indication that the dax page has been
> + * remapped UC to prevent speculative consumption of poison.
> + */
> + SetPageHWPoison(page);
> +
> + /*
> + * Unlike System-RAM there is no possibility to swap in a
> + * different physical page at a given virtual address, so all
> + * userspace consumption of ZONE_DEVICE memory necessitates
> + * SIGBUS (i.e. MF_MUST_KILL)
> + */
> + flags |= MF_ACTION_REQUIRED | MF_MUST_KILL;
> + collect_procs(page, &to_kill, true);
> +
> + unmap_and_kill(&to_kill, pfn, page->mapping, page->index, flags);
> +unlock:
> + dax_unlock_page(page, cookie);
> + return rc;
> +}
> +
> /*
> * Called from hugetlb code with hugetlb_lock held.
> *
> @@ -1644,12 +1728,8 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
> struct dev_pagemap *pgmap)
> {
> struct page *page = pfn_to_page(pfn);
> - unsigned long size = 0;
> - struct to_kill *tk;
> LIST_HEAD(tokill);

Is this variable unused in this function?

Thanks,
Naoya Horiguchi