On Mon, Jul 05, 2021 at 07:33:35PM +0800, Chao Yu wrote:
> On 2021/7/5 16:56, Jaegeuk Kim wrote:
> > On 07/05, Chao Yu wrote:
> > > On 2021/7/5 13:22, Jaegeuk Kim wrote:
> > > > We need to guarantee it's initially zero. Otherwise, it'll hurt entire flag
> > > > operations.
> > >
> > > Oops, I didn't get the point, shouldn't .private be zero after page was
> > > just allocated by filesystem? What's the case we will encounter stall
> > > private data left in page?
> >
> > I'm seeing f2fs_migrate_page() has the newpage with some value without Private
> > flag. That causes a kernel panic later due to wrong private flag used in f2fs.
>
> I'm not familiar with that part of codes, so Cc mm mailing list for help.
>
> My question is newpage in .migrate_page() may contain non-zero value in .private
> field but w/o setting PagePrivate flag, is it a normal case?
I think freshly allocated pages have a page->private of 0. ie this
code in mm/page_alloc.c:
page = rmqueue(ac->preferred_zoneref->zone, zone, order,
gfp_mask, alloc_flags, ac->migratetype);
if (page) {
prep_new_page(page, order, gfp_mask, alloc_flags);
where prep_new_page() calls post_alloc_hook() which contains:
set_page_private(page, 0);
Now, I do see in __buffer_migrate_page() (mm/migrate.c):
attach_page_private(newpage, detach_page_private(page));
but as far as I can tell, f2fs doesn't call any of the
buffer_migrate_page() paths. So I'm not sure why you're seeing
a non-zero page->private.
