On Fri, Nov 8, 2024 at 4:10 PM Shakeel Butt <shakeel.butt@xxxxxxxxx> wrote:
>
> On Thu, Nov 07, 2024 at 03:56:09PM -0800, Joanne Koong wrote:
> > Add a new mapping flag AS_WRITEBACK_MAY_BLOCK which filesystems may set
> > to indicate that writeback operations may block or take an indeterminate
> > amount of time to complete. Extra caution should be taken when waiting
> > on writeback for folios belonging to mappings where this flag is set.
> >
> > Signed-off-by: Joanne Koong <joannelkoong@xxxxxxxxx>
> > ---
> > include/linux/pagemap.h | 11 +++++++++++
> > 1 file changed, 11 insertions(+)
> >
> > diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> > index 68a5f1ff3301..eb5a7837e142 100644
> > --- a/include/linux/pagemap.h
> > +++ b/include/linux/pagemap.h
> > @@ -210,6 +210,7 @@ enum mapping_flags {
> > AS_STABLE_WRITES = 7, /* must wait for writeback before modifying
> > folio contents */
> > AS_INACCESSIBLE = 8, /* Do not attempt direct R/W access to the mapping */
> > + AS_WRITEBACK_MAY_BLOCK = 9, /* Use caution when waiting on writeback */
>
> To me 'may block' does not feel right. For example in reclaim code,
> folio_wait_writeback() can get blocked and that is fine. However with
> non-privileged fuse involved, there are security concerns. Somehow 'may
> block' does not convey that. Anyways, I am not really pushing back but
> I think there is a need for better name here.
Ahh I see where this naming causes confusion - the "MAY_BLOCK" part
could be interpreted in two ways: a) may block as in it's possible for
the writeback to block and b) may block as in it's permissible/ok for
the writeback to block. I intended "may block" to signify a) but
you're right, it could be easily interpreted as b).
I'll change this to AS_WRITEBACK_BLOCKING.
Thanks,
Joanne
>
> > /* Bits 16-25 are used for FOLIO_ORDER */
> > AS_FOLIO_ORDER_BITS = 5,
> > AS_FOLIO_ORDER_MIN = 16,
> > @@ -335,6 +336,16 @@ static inline bool mapping_inaccessible(struct address_space *mapping)
> > return test_bit(AS_INACCESSIBLE, &mapping->flags);
> > }
> >
> > +static inline void mapping_set_writeback_may_block(struct address_space *mapping)
> > +{
> > + set_bit(AS_WRITEBACK_MAY_BLOCK, &mapping->flags);
> > +}
> > +
> > +static inline bool mapping_writeback_may_block(struct address_space *mapping)
> > +{
> > + return test_bit(AS_WRITEBACK_MAY_BLOCK, &mapping->flags);
> > +}
> > +
> > static inline gfp_t mapping_gfp_mask(struct address_space * mapping)
> > {
> > return mapping->gfp_mask;
> > --
> > 2.43.5
> >
