linux-kernel - Re: [RESEND PATCH V5 00/33] block: support multipage bvec

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Date:   Sun, 27 May 2018 19:44:52 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Ming Lei <ming.lei@...hat.com>
Cc:     Kent Overstreet <kent.overstreet@...il.com>,
        Christoph Hellwig <hch@...radead.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        David Sterba <dsterba@...e.cz>,
        Huang Ying <ying.huang@...el.com>,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        Theodore Ts'o <tytso@....edu>,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        Coly Li <colyli@...e.de>, Filipe Manana <fdmanana@...il.com>
Subject: Re: [RESEND PATCH V5 00/33] block: support multipage bvec

On 5/27/18 1:23 AM, Ming Lei wrote:
> On Fri, May 25, 2018 at 10:30:46AM -0600, Jens Axboe wrote:
>> On 5/24/18 10:53 PM, Kent Overstreet wrote:
>>> On Fri, May 25, 2018 at 11:45:48AM +0800, Ming Lei wrote:
>>>> Hi,
>>>>
>>>> This patchset brings multipage bvec into block layer:
>>>
>>> patch series looks sane to me. goddamn that's a lot of renaming.
>>
>> Indeed... I actually objected to some of the segment -> page
>> renaming, but it's still in there. The foo2() temporary functions
>> also concern me, we all know there's nothing more permanent than a
>> temporary fixup.
> 
> Jens, I remember I explained the renaming story to you in lsfmm a bit:
> 
> 1) the current naming of segment is actually wrong, since every segment
> only stores one single-page vector
> 
> 2) the most important part is that once multipage bvec is introduced,
> if the old _segment naming is still kept, it can be very confusing,
> especially no good name is left for the helpers of dealing with real
> segment.

Yes, we discussed exactly this, which is why I'm surprised you went
ahead with the same approach. I told you I don't like tree wide renames,
if they can be avoided. I'd rather suffer some pain wrt page vs segments
naming, and then later do a rename (if it bothers us) once the dust has
settled on the interesting part of the changes.

I'm very well away of our current naming and what it signifies.  With
#1, you are really splitting hairs, imho. Find a decent name for
multiple segment. Chunk?

> For the foo2() temporary change, that is only for avoiding tree-wide
> change in one single tree, with this way, we can change sub-system one
> by one, but if you think it is good to do tree-wide conversion in one
> patch, I am fine to do it in next version.

It's still a painful middle step.

>>> Things are going to get interesting when we start sticking compound
>>> pages in the page cache, there'll be some interesting questions of
>>> semantics to deal with then but I think getting this will only help
>>> w.r.t. plumbing that through and not dealing with 4k pages
>>> unnecessarily - but I think even if we were to decide that merging
>>> in bio_add_page() is not the way to go when the upper layers are
>>> passing compound pages around already, this patch series helps
>>> because regardless at some point everything under
>>> generic_make_request() is going to have to deal with segments that
>>> are more than one page, and this patch series makes that happen. So
>>> incremental progress.
>>>
>>> Jens, any objections to getting this in?
>>
>> I like most of it, but I'd much rather get this way earlier in the
>> series.  We're basically just one week away from the merge window, it
>> needs more simmer and testing time than that. On top of that, it
>> hasn't received much review yet.
>>
>> So as far as I'm concerned, we can kick off the 4.19 block branch
>> with iterated versions of this patchset.
> 
> OK, I will post out again once v4.19 is started.

Sounds good.

-- 
Jens Axboe