[CC'ing authors of the code plus mm folks] Am Freitag, 14. Dezember 2018, 06:56:01 CET schrieb zhangjun: > IOMAP uses PG_private a little different with buffer_head based > filesystem. > It uses it as marker and when set, the page counter is not incremented, > migrate_page_move_mapping() assumes that PG_private indicates a counter > of +1. > so, we have to pass a extra count of -1 to migrate_page_move_mapping() > if the flag is set. > > Signed-off-by: zhangjun <[email protected]> > --- > fs/iomap.c | 11 ++++++++++- > 1 file changed, 10 insertions(+), 1 deletion(-) > > diff --git a/fs/iomap.c b/fs/iomap.c > index 64ce240..352e58a 100644 > --- a/fs/iomap.c > +++ b/fs/iomap.c > @@ -544,8 +544,17 @@ iomap_migrate_page(struct address_space *mapping, struct > page *newpage, > struct page *page, enum migrate_mode mode) > { > int ret; > + int extra_count = 0; > > - ret = migrate_page_move_mapping(mapping, newpage, page, NULL, mode, 0); > + /* > + * IOMAP uses PG_private as marker and does not raise the page counter. > + * migrate_page_move_mapping() expects a incremented counter if > PG_private > + * is set. Therefore pass -1 as extra_count for this case. > + */ > + if (page_has_private(page)) > + extra_count = -1; > + ret = migrate_page_move_mapping(mapping, newpage, page, > + NULL, mode, extra_count); > if (ret != MIGRATEPAGE_SUCCESS) > return ret;
This is the third place which needs this workaround. UBIFS, F2FS, and now iomap. I agree with Dave that nobody can assume that PG_private implies an additional page reference. But page migration does that. Including parts of the write back code. Thanks, //richard
