Re: [Chapter One] THP zones: the use cases of policy zones

[Yu Zhao <yuzhao@google.com>]

On Thu, Oct 31, 2024 at 8:35 PM Charan Teja Kalla
<quic_charante@quicinc.com> wrote:
>
> Hi Yu,
>
> On 3/1/2024 12:04 AM, Yu Zhao wrote:
> > diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> > index de292a007138..c0f9d21b4d18 100644
> > --- a/include/linux/gfp.h
> > +++ b/include/linux/gfp.h
> > @@ -88,8 +88,8 @@ static inline bool gfpflags_allow_blocking(const gfp_t gfp_flags)
> >   * GFP_ZONES_SHIFT must be <= 2 on 32 bit platforms.
> >   */
> >
> > -#if defined(CONFIG_ZONE_DEVICE) && (MAX_NR_ZONES-1) <= 4
> > -/* ZONE_DEVICE is not a valid GFP zone specifier */
> > +#if MAX_NR_ZONES - 2 - IS_ENABLED(CONFIG_ZONE_DEVICE) <= 4
> > +/* zones beyond ZONE_MOVABLE are not valid GFP zone specifiers */
> >  #define GFP_ZONES_SHIFT 2
> >  #else
> >  #define GFP_ZONES_SHIFT ZONES_SHIFT
> > @@ -135,9 +135,29 @@ static inline enum zone_type gfp_zone(gfp_t flags)
> >       z = (GFP_ZONE_TABLE >> (bit * GFP_ZONES_SHIFT)) &
> >                                        ((1 << GFP_ZONES_SHIFT) - 1);
> >       VM_BUG_ON((GFP_ZONE_BAD >> bit) & 1);
> > +
> > +     if ((flags & (__GFP_MOVABLE | __GFP_COMP)) == (__GFP_MOVABLE | __GFP_COMP))
> > +             return LAST_VIRT_ZONE;
> > +
> Not sure If someone had already reported this: With this patch, we allow
> pages to allocate from movable zone(through fallback from
> LAST_VIRT_ZONE) even with out __GFP_HIGHMEM. The commit cc09cb134124a
> ("mm/page_alloc: Add folio allocation functions") sets the __GFP_COMP by
> default and user has just to pass the __GFP_MOVABLE. Please CMIW.

Hi Charan,

I don't remember whether we have this fixed in the Android kernel off
the top of head -- I'll ask Kalesh to take a closer look and follow up
with you.

Thanks!