From: Yu Zhao <yuzhao@google.com>
To: Michal Hocko <mhocko@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Alex Shi <alex.shi@linux.alibaba.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ingo Molnar <mingo@redhat.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Vladimir Davydov <vdavydov.dev@gmail.com>,
Roman Gushchin <guro@fb.com>, Shakeel Butt <shakeelb@google.com>,
Chris Down <chris@chrisdown.name>,
Yafang Shao <laoar.shao@gmail.com>,
Vlastimil Babka <vbabka@suse.cz>,
Huang Ying <ying.huang@intel.com>,
Pankaj Gupta <pankaj.gupta.linux@gmail.com>,
Matthew Wilcox <willy@infradead.org>,
Konstantin Khlebnikov <koct9i@gmail.com>,
Minchan Kim <minchan@kernel.org>,
Jaewon Kim <jaewon31.kim@samsung.com>,
cgroups@vger.kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 00/13] mm: clean up some lru related pieces
Date: Fri, 18 Sep 2020 03:36:31 -0600 [thread overview]
Message-ID: <20200918093631.GA987554@google.com> (raw)
In-Reply-To: <20200918074549.GG28827@dhcp22.suse.cz>
On Fri, Sep 18, 2020 at 09:45:49AM +0200, Michal Hocko wrote:
> On Thu 17-09-20 21:00:38, Yu Zhao wrote:
> > Hi Andrew,
> >
> > I see you have taken this:
> > mm: use add_page_to_lru_list()/page_lru()/page_off_lru()
> > Do you mind dropping it?
> >
> > Michal asked to do a bit of additional work. So I thought I probably
> > should create a series to do more cleanups I've been meaning to.
> >
> > This series contains the change in the patch above and goes a few
> > more steps farther. It's intended to improve readability and should
> > not have any performance impacts. There are minor behavior changes in
> > terms of debugging and error reporting, which I have all highlighted
> > in the individual patches. All patches were properly tested on 5.8
> > running Chrome OS, with various debug options turned on.
> >
> > Michal,
> >
> > Do you mind taking a looking at the entire series?
>
> I have stopped at patch 3 as all patches until then are really missing
> any justification. What is the point for all this to be done? The code
> is far from trivial and just shifting around sounds like a risk. You are
I appreciate your caution, and if you let me know what exactly your
concerns are, we could probably work them out together.
> removing ~50 LOC which is always nice but I am not sure the resulting
> code is better maintainble or easier to read and understand. Just
> consider __ClearPageLRU moving to page_off_lru patch. What is the
> additional value of having the flag moved and burry it into a function
> to have even more side effects? I found the way how __ClearPageLRU is
Mind elaborating the side effects?
> nicely close to removing it from LRU easier to follow. This is likely
> subjective and other might think differently but as it is not clear what
> is your actual goal here it is hard to judge pros and cons.
I like this specific example from patch 3. Here is what it does: we
have three places using the same boilerplate, i.e., page_off_lru() +
__ClearPageLRU(), the patch moves __ClearPageLRU() into page_off_lru(),
which already does __ClearPageActive() and __ClearPageUnevictable().
Later on, we rename page_off_lru() to __clear_page_lru_flags() (patch
8).
Its point seems quite clear to me. Why would *anybody* want to use
two helper functions *repeatedly* when the job can be done with just
one? Nobody is paid by the number of lines they add, right? :) And
for that matter, why would anybody want any boilerplate to be open
coded from the same group of helper functions arranged in various
ways? I don't think the answer is subjective, but I don't expect
everybody to agree with me.
Now back to your general question: what's the point of this series?
Readability -- less error prone and easier to maintain. This series
consolidate open-coded boilerplate like the following in many places.
Take lru_lazyfree_fn() as an example:
- bool active = PageActive(page);
int nr_pages = thp_nr_pages(page);
- del_page_from_lru_list(page, lruvec,
- LRU_INACTIVE_ANON + active);
+ del_page_from_lru_list(page, lruvec);
ClearPageActive(page);
ClearPageReferenced(page);
<snipped>
ClearPageSwapBacked(page);
- add_page_to_lru_list(page, lruvec, LRU_INACTIVE_FILE);
+ add_page_to_lru_list(page, lruvec);
I hope this helps, but if it doesn't, I'd be more than happy to have
more discussions on the details. And not that I don't appreciate your
review, but please be more specific than 'sounds like a risk' or 'have
even more side effects' so I can address your concerns effectively.
next prev parent reply other threads:[~2020-09-18 9:36 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-18 3:00 [PATCH 00/13] mm: clean up some lru related pieces Yu Zhao
2020-09-18 3:00 ` [PATCH 01/13] mm: use add_page_to_lru_list() Yu Zhao
2020-09-18 7:32 ` Michal Hocko
2020-09-18 10:05 ` Yu Zhao
2020-09-18 3:00 ` [PATCH 02/13] mm: use page_off_lru() Yu Zhao
2020-09-18 7:37 ` Michal Hocko
2020-09-18 10:27 ` Yu Zhao
2020-09-18 11:09 ` Michal Hocko
2020-09-18 18:53 ` Yu Zhao
2020-09-21 11:16 ` Michal Hocko
2020-09-18 11:24 ` Michal Hocko
2020-09-18 3:00 ` [PATCH 03/13] mm: move __ClearPageLRU() into page_off_lru() Yu Zhao
2020-09-18 7:38 ` Michal Hocko
2020-09-18 3:00 ` [PATCH 04/13] mm: shuffle lru list addition and deletion functions Yu Zhao
2020-09-18 3:00 ` [PATCH 05/13] mm: don't pass enum lru_list to lru list addition functions Yu Zhao
2020-09-18 3:00 ` [PATCH 06/13] mm: don't pass enum lru_list to trace_mm_lru_insertion() Yu Zhao
2020-09-18 3:00 ` [PATCH 07/13] mm: don't pass enum lru_list to del_page_from_lru_list() Yu Zhao
2020-09-18 3:00 ` [PATCH 08/13] mm: rename page_off_lru() to __clear_page_lru_flags() Yu Zhao
2020-09-18 3:00 ` [PATCH 09/13] mm: inline page_lru_base_type() Yu Zhao
2020-09-18 3:00 ` [PATCH 10/13] mm: VM_BUG_ON lru page flags Yu Zhao
2020-09-18 3:00 ` [PATCH 11/13] mm: inline __update_lru_size() Yu Zhao
2020-09-18 3:00 ` [PATCH 12/13] mm: make lruvec_lru_size() static Yu Zhao
2020-09-18 3:00 ` [PATCH 13/13] mm: enlarge the int parameter of update_lru_size() Yu Zhao
2020-09-18 7:45 ` [PATCH 00/13] mm: clean up some lru related pieces Michal Hocko
2020-09-18 9:36 ` Yu Zhao [this message]
2020-09-18 20:46 ` Hugh Dickins
2020-09-18 21:01 ` Yu Zhao
2020-09-18 21:19 ` Hugh Dickins
2020-09-19 0:31 ` Alex Shi
2020-10-13 2:30 ` Hugh Dickins
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