linux-kernel - Re: cleanup the walk_page

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Message-ID: <c5e7dbac-2d40-60fa-00cc-a275b3aa8373@shipmail.org>
Date:   Fri, 9 Aug 2019 00:21:24 +0200
From:   Thomas Hellstrom <thomas@...pmail.org>
To:     Christoph Hellwig <hch@....de>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Jerome Glisse <jglisse@...hat.com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Steven Price <steven.price@....com>,
        Linux-MM <linux-mm@...ck.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>
Subject: Re: cleanup the walk_page_range interface

On 8/8/19 11:56 PM, Christoph Hellwig wrote:
> On Thu, Aug 08, 2019 at 10:50:37AM -0700, Linus Torvalds wrote:
>>> Note that both Thomas and Steven have series touching this area pending,
>>> and there are a couple consumer in flux too - the hmm tree already
>>> conflicts with this series, and I have potential dma changes on top of
>>> the consumers in Thomas and Steven's series, so we'll probably need a
>>> git tree similar to the hmm one to synchronize these updates.
>> I'd be willing to just merge this now, if that helps. The conversion
>> is mechanical, and my only slight worry would be that at least for my
>> original patch I didn't build-test the (few) non-x86
>> architecture-specific cases. But I did end up looking at them fairly
>> closely  (basically using some grep/sed scripts to see that the
>> conversions I did matched the same patterns). And your changes look
>> like obvious improvements too where any mistake would have been caught
>> by the compiler.
> I did cross compile the s390 and powerpc bits, but I do not have an
> openrisc compiler.
>
>> So I'm not all that worried from a functionality standpoint, and if
>> this will help the next merge window, I'll happily pull now.
> That would help with this series vs the others, but not with the other
> series vs each other.

Although my series doesn't touch the pagewalk code, it rather borrowed 
some concepts from it and used for the apply_to_page_range() interface.

The reason being that the pagewalk code requires the mmap_sem to be held 
(mainly for trans-huge pages and reading the vma->vm_flags if I 
understand the code correctly). That is fine when you scan the vmas of a 
process, but the helpers I wrote need to instead scan all vmas pointing 
into a struct address_space, and taking the mmap_sem for each vma will 
create lock inversion problems.

/Thomas