linux-kernel - Re: [PATCH RFC v3 11/35] mm: Allow an arch to hook into folio allocation when VMA is known

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Date: Mon, 29 Jan 2024 11:59:21 +0000
From: Alexandru Elisei <alexandru.elisei@....com>
To: Peter Collingbourne <pcc@...gle.com>
Cc: catalin.marinas@....com, will@...nel.org, oliver.upton@...ux.dev,
	maz@...nel.org, james.morse@....com, suzuki.poulose@....com,
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	linux-mm@...ck.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH RFC v3 11/35] mm: Allow an arch to hook into folio
 allocation when VMA is known

Hi Peter,

On Fri, Jan 26, 2024 at 12:00:36PM -0800, Peter Collingbourne wrote:
> On Thu, Jan 25, 2024 at 8:43 AM Alexandru Elisei
> <alexandru.elisei@....com> wrote:
> >
> > arm64 uses VM_HIGH_ARCH_0 and VM_HIGH_ARCH_1 for enabling MTE for a VMA.
> > When VM_HIGH_ARCH_0, which arm64 renames to VM_MTE, is set for a VMA, and
> > the gfp flag __GFP_ZERO is present, the __GFP_ZEROTAGS gfp flag also gets
> > set in vma_alloc_zeroed_movable_folio().
> >
> > Expand this to be more generic by adding an arch hook that modifes the gfp
> > flags for an allocation when the VMA is known.
> >
> > Note that __GFP_ZEROTAGS is ignored by the page allocator unless __GFP_ZERO
> > is also set; from that point of view, the current behaviour is unchanged,
> > even though the arm64 flag is set in more places.  When arm64 will have
> > support to reuse the tag storage for data allocation, the uses of the
> > __GFP_ZEROTAGS flag will be expanded to instruct the page allocator to try
> > to reserve the corresponding tag storage for the pages being allocated.
> >
> > The flags returned by arch_calc_vma_gfp() are or'ed with the flags set by
> > the caller; this has been done to keep an architecture from modifying the
> > flags already set by the core memory management code; this is similar to
> > how do_mmap() -> calc_vm_flag_bits() -> arch_calc_vm_flag_bits() has been
> > implemented. This can be revisited in the future if there's a need to do
> > so.
> >
> > Signed-off-by: Alexandru Elisei <alexandru.elisei@....com>
> 
> This patch also needs to update the non-CONFIG_NUMA definition of
> vma_alloc_folio in include/linux/gfp.h to call arch_calc_vma_gfp. See:
> https://r.android.com/2849146

Of course, you're already reported this to me, I cherry-pick the version of
the patch that doesn't have the fix for this series.

Will fix.

Thanks,
Alex

> 
> Peter