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    SubjectRe: [PATCH 2/2] mm: Add kvmalloc_ab_c and kvzalloc_struct


    On Thu, 8 Mar 2018, Matthew Wilcox wrote:

    > 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?

    Is the use of vmalloc a necessary part of the design? Or could there be a
    non vmalloc versions for call sites that are already ok with that?

    julia

    > > 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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