On Fri, 2020-11-06 at 11:05 +0800, Hillf Danton wrote:
> On Thu, 5 Nov 2020 14:15:08 -0500
> > Matthew Wilcox pointed out that the i915 driver opportunistically
> > allocates tmpfs memory, but will happily reclaim some of its
> > pool if no memory is available.
> >
> > Make sure the gfp mask used to opportunistically allocate a THP
> > is always at least as restrictive as the original gfp mask.
> >
> > Signed-off-by: Rik van Riel <riel@xxxxxxxxxxx>
> > Suggested-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> > ---
> > mm/shmem.c | 21 +++++++++++++++++++++
> > 1 file changed, 21 insertions(+)
> >
> > diff --git a/mm/shmem.c b/mm/shmem.c
> > index 6c3cb192a88d..ee3cea10c2a4 100644
> > --- a/mm/shmem.c
> > +++ b/mm/shmem.c
> > @@ -1531,6 +1531,26 @@ static struct page *shmem_swapin(swp_entry_t
> > swap, gfp_t gfp,
> > return page;
> > }
> >
> > +/*
> > + * Make sure huge_gfp is always more limited than limit_gfp.
> > + * Some of the flags set permissions, while others set
> > limitations.
> > + */
> > +static gfp_t limit_gfp_mask(gfp_t huge_gfp, gfp_t limit_gfp)
> > +{
> > + gfp_t allowflags = __GFP_IO | __GFP_FS | __GFP_RECLAIM;
> > + gfp_t denyflags = __GFP_NOWARN | __GFP_NORETRY;
> > + gfp_t result = huge_gfp & ~allowflags;
> > +
> > + /*
> > + * Minimize the result gfp by taking the union with the deny
> > flags,
> > + * and the intersection of the allow flags.
> > + */
> > + result |= (limit_gfp & denyflags);
>
> Currently NORETRY is always set regardless of i915 and if it's
> determined in 1/2 then the i915 thing can be done like
>
> return huge_gfp | (limit_gfp & __GFP_RECLAIM);
No, if __GFP_KSWAPD_RECLAIM or __GFP_DIRECT_RECLAIM are
not set in either huge_gfp or limit_gfp, we want to ensure
the resulting gfp does not have it set, either.
Your suggested change
would result in __GFP_KSWAPD_RECLAIM
or __GFP_DIRECT_RECLAIM getting set if it was set in either
of the input gfp variables, which is probably not the desired
behavior.
--
All Rights Reversed.
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