Re: [PATCH] doc: mm: migration doesn't use FOLL_SPLIT anymore

From: Zi Yan
Date: Thu Apr 18 2019 - 16:30:37 EST

On 18 Apr 2019, at 16:17, Yang Shi wrote:

When demonstrating FOLL_SPLIT in transhuge document, migration is used
as an example. But, since commit 94723aafb9e7 ("mm: unclutter THP
migration"), the way of THP migration is totally changed. FOLL_SPLIT is
not used by migration anymore due to the change.

Remove the obsolete example to avoid confusion.

Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Zi Yan <ziy@xxxxxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
Documentation/vm/transhuge.rst | 8 +-------
1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/Documentation/vm/transhuge.rst b/Documentation/vm/transhuge.rst
index a8cf680..8df3806 100644
--- a/Documentation/vm/transhuge.rst
+++ b/Documentation/vm/transhuge.rst
@@ -55,13 +55,7 @@ prevent page from being split by anyone.
In case you can't handle compound pages if they're returned by
follow_page, the FOLL_SPLIT bit can be specified as parameter to
follow_page, so that it will split the hugepages before returning
-them. Migration for example passes FOLL_SPLIT as parameter to
-follow_page because it's not hugepage aware and in fact it can't work
-at all on hugetlbfs (but it instead works fine on transparent
-hugepages thanks to FOLL_SPLIT). migration simply can't deal with
-hugepages being returned (as it's not only checking the pfn of the
-page and pinning it during the copy but it pretends to migrate the
-memory in regular page sizes and with regular pte/pmd mappings).

Graceful fallback

Thanks for updating the document.

Reviewed-by: Zi Yan <ziy@xxxxxxxxxx>

Best Regards,
Yan Zi