linux-kernel - Re: [PATCH 0/2] z3fold fixes

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Date:   Thu, 22 Dec 2016 16:55:54 -0500
From:   Dan Streetman <ddstreet@...e.org>
To:     Vitaly Wool <vitalywool@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux-MM <linux-mm@...ck.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Dan Carpenter <dan.carpenter@...cle.com>
Subject: Re: [PATCH 0/2] z3fold fixes

On Sun, Dec 18, 2016 at 3:15 AM, Vitaly Wool <vitalywool@...il.com> wrote:
> On Tue, Nov 29, 2016 at 11:39 PM, Andrew Morton
> <akpm@...ux-foundation.org> wrote:
>> On Tue, 29 Nov 2016 17:33:19 -0500 Dan Streetman <ddstreet@...e.org> wrote:
>>
>>> On Sat, Nov 26, 2016 at 2:15 PM, Vitaly Wool <vitalywool@...il.com> wrote:
>>> > Here come 2 patches with z3fold fixes for chunks counting and locking. As commit 50a50d2 ("z3fold: don't fail kernel build is z3fold_header is too big") was NAK'ed [1], I would suggest that we removed that one and the next z3fold commit cc1e9c8 ("z3fold: discourage use of pages that weren't compacted") and applied the coming 2 instead.
>>>
>>> Instead of adding these onto all the previous ones, could you redo the
>>> entire z3fold series?  I think it'll be simpler to review the series
>>> all at once and that would remove some of the stuff from previous
>>> patches that shouldn't be there.
>>>
>>> If that's ok with Andrew, of course, but I don't think any of the
>>> z3fold patches have been pushed to Linus yet.
>>
>> Sounds good to me.  I had a few surprise rejects when merging these
>> two, which indicates that things might be out of sync.
>>
>> I presently have:
>>
>> z3fold-limit-first_num-to-the-actual-range-of-possible-buddy-indexes.patch
>> z3fold-make-pages_nr-atomic.patch
>> z3fold-extend-compaction-function.patch
>> z3fold-use-per-page-spinlock.patch
>> z3fold-discourage-use-of-pages-that-werent-compacted.patch
>> z3fold-fix-header-size-related-issues.patch
>> z3fold-fix-locking-issues.patch
>
> My initial suggestion was to have it the following way:
> z3fold-limit-first_num-to-the-actual-range-of-possible-buddy-indexes.patch

this is a good one, acked by both of us; it should stay and go upstream to Linus

> z3fold-make-pages_nr-atomic.patch

the change itself looks ok and I acked it, but as Andrew commented the
log says nothing about why it's being changed; the atomic function is
slower so the log should explain why it's being changed; anyone
reviewing the log history won't know why you made the change, and the
change all by itself is a step backwards in performance.

> z3fold-extend-compaction-function.patch

this explictly has a bug in it that's fixed in one of the later
patches; instead, this should be fixed up and resent.

> z3fold-use-per-page-spinlock.patch

i should have explicitly nak'ed this, as not only did it add a bug
(fixed by the the other 'fix-' patch below) but its design should be
replaced by kref counting, which your latest patch is working
towards...

> z3fold-fix-header-size-related-issues.patch
> z3fold-fix-locking-issues.patch

and these fix the known problems in the previous patches.

>
> I would prefer to keep the fix-XXX patches separate since e. g.
> z3fold-fix-header-size-related-issues.patch concerns also the problems
> that have been in the code for a while now. I am ok with folding these
> into the relevant main patches but once again, given that some fixes
> are related to the code that is already merged, I don't see why it
> would be better.

none of those patches are "merged", the last z3fold patch in Linus'
tree is 43afc194 from June.  Just because they're in Andrew's mmotm
queue (and/or linux-next) doesn't mean they are going to be
merged...(correct me please if I'm wrong there Andrew)

So as you can see by my patch-by-patch breakdown, almost all of them
need changes based on feedback from various people.  And they are all
related - your goal is to improve z3fold performance, right?  IMHO
they should be sent as a single patch series with that goal in the
cover letter, including specific details and numbers about how the
series does improve performance.

>
> ~vitaly
>
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