linux-kernel - Re: Linux 4.18-rc7

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Date:   Wed, 1 Aug 2018 23:51:56 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Tony Luck <tony.luck@...el.com>,
        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 01, 2018 at 01:05:48PM -0700, Linus Torvalds wrote:
> 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?

Is there a reason why we pass vma to flush_tlb_range?

It's not obvious to me what information from VMA can be useful for an
implementation. I see that ecard.c initialize vm_flags too, but it seems
unused by flush_tlb_range.

Maybe it's cleaner to have generic helper flush_tlb_range_mm() or
something?

In longer term we can change the interface to take mm instead of vma.

-- 
 Kirill A. Shutemov