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

Shiyang Ruan
2022-04-21T08:10:16Z

在 2022/4/21 14:13, HORIGUCHI NAOYA(堀口 直也) 写道:
> 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?

Yes, this one and the one above are mistakes I didn't notice when I
resolving conflicts with the newer next- branch. I'll fix them in next
version.

--
Thanks,
Ruan.

>
> Thanks,
> Naoya Horiguchi