On 26 Feb 2021, at 2:18, Alistair Popple wrote:
> Migration is currently implemented as a mode of operation for
> try_to_unmap_one() generally specified by passing the TTU_MIGRATION flag
> or in the case of splitting a huge anonymous page TTU_SPLIT_FREEZE.
>
> However it does not have much in common with the rest of the unmap
> functionality of try_to_unmap_one() and thus splitting it into a
> separate function reduces the complexity of try_to_unmap_one() making it
> more readable.
>
> Several simplifications can also be made in try_to_migrate_one() based
> on the following observations:
>
> - All users of TTU_MIGRATION also set TTU_IGNORE_MLOCK.
> - No users of TTU_MIGRATION ever set TTU_IGNORE_HWPOISON.
> - No users of TTU_MIGRATION ever set TTU_BATCH_FLUSH.
>
> TTU_SPLIT_FREEZE is a special case of migration used when splitting an
> anonymous page. This is most easily dealt with by calling the correct
> function from unmap_page() in mm/huge_memory.c - either
> try_to_migrate() for PageAnon or try_to_unmap().
>
> Signed-off-by: Alistair Popple <apopple@xxxxxxxxxx>
> ---
> include/linux/rmap.h | 4 +-
> mm/huge_memory.c | 10 +-
> mm/migrate.c | 9 +-
> mm/rmap.c | 352 +++++++++++++++++++++++++++++++------------
> 4 files changed, 269 insertions(+), 106 deletions(-)
>
> diff --git a/include/linux/rmap.h b/include/linux/rmap.h
> index 7f1ee411bd7b..77fa17de51d7 100644
> --- a/include/linux/rmap.h
> +++ b/include/linux/rmap.h
> @@ -86,8 +86,6 @@ struct anon_vma_chain {
> };
>
> enum ttu_flags {
> - TTU_MIGRATION = 0x1, /* migration mode */
> -
> TTU_SPLIT_HUGE_PMD = 0x4, /* split huge PMD if any */
It implies freeze in try_to_migrate() and no freeze in try_to_unmap(). I think
we need some comments here, above try_to_migrate(), and above try_to_unmap()
to clarify the implication.
> TTU_IGNORE_MLOCK = 0x8, /* ignore mlock */
> TTU_IGNORE_HWPOISON = 0x20, /* corrupted page is recoverable */
> @@ -96,7 +94,6 @@ enum ttu_flags {
> * do a final flush if necessary */
> TTU_RMAP_LOCKED = 0x80, /* do not grab rmap lock:
> * caller holds it */
> - TTU_SPLIT_FREEZE = 0x100, /* freeze pte under splitting thp */
> };
>
> #ifdef CONFIG_MMU
> @@ -193,6 +190,7 @@ static inline void page_dup_rmap(struct page *page, bool compound)
> int page_referenced(struct page *, int is_locked,
> struct mem_cgroup *memcg, unsigned long *vm_flags);
>
> +bool try_to_migrate(struct page *page, enum ttu_flags flags);
> bool try_to_unmap(struct page *, enum ttu_flags flags);
>
> /* Avoid racy checks */
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index d00b93dc2d9e..357052a4567b 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2351,16 +2351,16 @@ void vma_adjust_trans_huge(struct vm_area_struct *vma,
>
> static void unmap_page(struct page *page)
> {
> - enum ttu_flags ttu_flags = TTU_IGNORE_MLOCK |
> - TTU_RMAP_LOCKED | TTU_SPLIT_HUGE_PMD;
> + enum ttu_flags ttu_flags = TTU_RMAP_LOCKED | TTU_SPLIT_HUGE_PMD;
> bool unmap_success;
>
> VM_BUG_ON_PAGE(!PageHead(page), page);
>
> if (PageAnon(page))
> - ttu_flags |= TTU_SPLIT_FREEZE;
> -
> - unmap_success = try_to_unmap(page, ttu_flags);
> + unmap_success = try_to_migrate(page, ttu_flags);
> + else
> + unmap_success = try_to_unmap(page, ttu_flags |
> + TTU_IGNORE_MLOCK);
I think we need a comment here about why anonymous pages need try_to_migrate()
and others need try_to_unmap().
Thanks.
—
Best Regards,
Yan Zi
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