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SubjectRe: [PATCH] MM: discard __GFP_ATOMIC
Date
On Thu, 18 Nov 2021, Matthew Wilcox wrote:
> On Wed, Nov 17, 2021 at 03:39:30PM +1100, NeilBrown wrote:
> > +++ b/drivers/iommu/tegra-smmu.c
> > @@ -676,12 +676,12 @@ static struct page *as_get_pde_page(struct tegra_smmu_as *as,
> > * allocate page in a sleeping context if GFP flags permit. Hence
> > * spinlock needs to be unlocked and re-locked after allocation.
> > */
> > - if (!(gfp & __GFP_ATOMIC))
> > + if (gfp & __GFP_DIRECT_RECLAIM)
> > spin_unlock_irqrestore(&as->lock, *flags);
> >
> > page = alloc_page(gfp | __GFP_DMA | __GFP_ZERO);
> >
> > - if (!(gfp & __GFP_ATOMIC))
> > + if (gfp & __GFP_DIRECT_RECLAIM)
> > spin_lock_irqsave(&as->lock, *flags);
> >
> > /*
>
> Surely this should be gfpflags_allow_blocking() instead of poking about
> in the innards of gfp flags?

Possibly. Didn't know about gfpflags_allow_blocking(). From a quick
grep in the kernel, a whole lot of other people don't know about it
either, though clearly some do.

Maybe we should reaname "__GFP_DIRECT_RECLAIM" to
"__GFP_ALLOW_BLOCKING", because that is what most users seems to care
about.

If not, then we probably want a gfpflags_without_block() function that
removes that flag, as lots of code wants to do that - and using the flag
for one, and an inline for the other is not consistent.

My leaning would be to __GFP_ALLOW_BLOCKING

NeilBrown


>
> This patch seems like a good simplification to me.
>
> Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>

Thanks,
NeilBrown

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