linux-kernel - Re: Linux 4.18-rc7

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Message-ID: <CA+55aFz0eKks=v872LA-tDx4qcmBtxTYXbeztZcWbgx6SeQHNg@mail.gmail.com>
Date:   Wed, 1 Aug 2018 13:05:48 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Tony Luck <tony.luck@...el.com>
Cc:     "Kirill A. Shutemov" <kirill@...temov.name>,
        Amit Pundir <amit.pundir@...aro.org>,
        John Stultz <john.stultz@...aro.org>,
        Hugh Dickins <hughd@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-mm <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        youling 257 <youling257@...il.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Colin Cross <ccross@...gle.com>
Subject: Re: Linux 4.18-rc7

On Wed, Aug 1, 2018 at 10:15 AM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> I'm still unhappy about the vma_init() ones, and I have not decided
> how to go with those. Either the memset() in vma_init(), or just
> reverting the (imho unnecessary) commit 2c4541e24c55. Kirill, Andrew,
> comments?

Ugh. Adding a memset looks simple, but screws up some places that have
other initialization. It also requires adding a new include of
<linux/string.h>, or we'd need to uninline vma_init() and put it
somewhere else.

But just reverting commit 2c4541e24c55 ("mm: use vma_init() to
initialize VMAs on stack and data segments") entirely isn't good
either, because some of the cases aren't about the TLB flush
interface, and call down to "real" VM functions. The 'pseudo_vma' use
of remove_inode_hugepages() and hugetlbfs_fallocate() in particular is
odd, but using vma_init() looks good there. And those places had the
memset() already.

So I'm inclined to simply mark the TLB-related vma_init() cases
special, and use something like this:

  #define TLB_FLUSH_VMA(mm,flags) { .vm_mm = (mm), .vm_flags = (flags) }

to make it very obvious when we're doing that vma initialization for
flush_tlb_range(). It's done as an initializer, exactly so that the
only valid syntax is to do somethin glike this:

        struct vm_area_struct vma = TLB_FLUSH_VMA(mm, VM_EXEC);

That leaves vma_init() users to be just the actual real allocation
path, and a few very specific specual vmas (the hugetlbfs and
mempolicy pseudo-vma, and a couple of "gate" vmas).

Suggested patch attached. Comments?

                 Linus

View attachment "patch.diff" of type "text/x-patch" (4025 bytes)