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SubjectRe: [PATCH 2/2] mm: Add kvmalloc_ab_c and kvzalloc_struct
On Thu, Mar 08, 2018 at 07:24:47AM +0100, Julia Lawall wrote:
> On Wed, 7 Mar 2018, Matthew Wilcox wrote:
> > On Wed, Mar 07, 2018 at 10:18:21PM +0100, Julia Lawall wrote:
> > > > Otherwise, yes, please. We could build a coccinelle rule for
> > > > additional replacements...
> > >
> > > A potential semantic patch and the changes it generates are attached
> > > below. Himanshu Jha helped with its development. Working on this
> > > uncovered one bug, where the allocated array is too large, because the
> > > size provided for it was a structure size, but actually only pointers to
> > > that structure were to be stored in it.
> >
> > This is cool! Thanks for doing the coccinelle patch! Diffstat:
> >
> > 50 files changed, 81 insertions(+), 124 deletions(-)
> >
> > I find that pretty compelling. I'll repost the kvmalloc_struct patch
> > imminently.
> Thanks. So it's OK to replace kmalloc and kzalloc, even though they
> didn't previously consider vmalloc and even though kmalloc doesn't zero?

We'll also need to replace the corresponding places where those structs
are freed with kvfree(). Can coccinelle handle that too?

> There are a few other cases that use GFP_NOFS and GFP_NOWAIT, but I didn't
> transform those because the comment says that the flags should be
> GFP_KERNEL based. Should those be transformed too?

The problem with non-GFP_KERNEL allocations is that vmalloc may have to
allocate page tables, which is always done with an implicit GFP_KERNEL
allocation. There's an intent to get rid of GFP_NOFS, but that's not
been realised yet (and I'm not sure of our strategy to eliminate it ...
I'll send a separate email about that). I'm not sure why anything's
trying to allocate with GFP_NOWAIT; can you send a list of those places?

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