From: Alex Shi <alex.shi@linux.alibaba.com>
To: Hugh Dickins <hughd@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
mgorman@techsingularity.net, tj@kernel.org,
khlebnikov@yandex-team.ru, daniel.m.jordan@oracle.com,
willy@infradead.org, hannes@cmpxchg.org, lkp@intel.com,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
cgroups@vger.kernel.org, shakeelb@google.com,
iamjoonsoo.kim@lge.com, richard.weiyang@gmail.com,
kirill@shutemov.name, alexander.duyck@gmail.com,
rong.a.chen@intel.com, mhocko@suse.com, vdavydov.dev@gmail.com,
shy828301@gmail.com, vbabka@suse.cz, minchan@kernel.org,
cai@lca.pw
Subject: Re: [PATCH v18 00/32] per memcg lru_lock: reviews
Date: Fri, 11 Sep 2020 10:50:56 +0800 [thread overview]
Message-ID: <855ad6ee-dba4-9729-78bd-23e392905cf6@linux.alibaba.com> (raw)
In-Reply-To: <alpine.LSU.2.11.2009091524260.10087@eggly.anvils>
在 2020/9/10 上午7:16, Hugh Dickins 写道:
> On Wed, 9 Sep 2020, Alex Shi wrote:
>> 在 2020/9/9 上午7:41, Hugh Dickins 写道:
>>>
>>> [PATCH v18 05/32] mm/thp: remove code path which never got into
>>> This is a good simplification, but I see no sign that you understand
>>> why it's valid: it relies on lru_add_page_tail() being called while
>>> head refcount is frozen to 0: we would not get this far if someone
>>> else holds a reference to the THP - which they must hold if they have
>>> isolated the page from its lru (and that's true before or after your
>>> per-memcg changes - but even truer after those changes, since PageLRU
>>> can then be flipped without lru_lock at any instant): please explain
>>> something of this in the commit message.
>>
>> Is the following commit log better?
>>
>> split_huge_page() will never call on a page which isn't on lru list, so
>> this code never got a chance to run, and should not be run, to add tail
>> pages on a lru list which head page isn't there.
>>
>> Hugh Dickins' mentioned:
>> The path should never be called since lru_add_page_tail() being called
>> while head refcount is frozen to 0: we would not get this far if someone
>> else holds a reference to the THP - which they must hold if they have
>> isolated the page from its lru.
>>
>> Although the bug was never triggered, it'better be removed for code
>> correctness, and add a warn for unexpected calling.
>
> Not much better, no. split_huge_page() can easily be called for a page
> which is not on the lru list at the time,
Hi Hugh,
Thanks for comments!
There are some discussion on this point a couple of weeks ago,
https://lkml.org/lkml/2020/7/9/760
Matthew Wilcox and Kirill have the following comments,
> I don't understand how we get to split_huge_page() with a page that's
> not on an LRU list. Both anonymous and page cache pages should be on
> an LRU list. What am I missing?
Right, and it's never got removed from LRU during the split. The tail
pages have to be added to LRU because they now separate from the tail
page.
--
Kirill A. Shutemov
> and I don't know what was the
> bug which was never triggered.
So the only path to the removed part should be a bug, like sth here,
https://lkml.org/lkml/2020/7/10/118
or
https://lkml.org/lkml/2020/7/10/972
> Stick with whatever text you end up with
> for the combination of 05/32 and 18/32, and I'll rewrite it after.
I am not object to merge them into one, I just don't know how to say
clear about 2 patches in commit log. As patch 18, TestClearPageLRU
add the incorrect posibility of remove lru bit during split, that's
the reason of code path rewrite and a WARN there.
Thanks
Alex
>
>>> [PATCH v18 06/32] mm/thp: narrow lru locking
>>> Why? What part does this play in the series? "narrow lru locking" can
>>> also be described as "widen page cache locking":
>>
>> Uh, the page cache locking isn't widen, it's still on the old place.
>
> I'm not sure if you're joking there. Perhaps just a misunderstanding.
>
> Yes, patch 06/32 does not touch the xa_lock(&mapping->i_pages) and
> xa_lock(&swap_cache->i_pages) lines (odd how we've arrived at two of
> those, but please do not get into cleaning it up now); but it removes
> the spin_lock_irqsave(&pgdata->lru_lock, flags) which used to come
> before them, and inserts a spin_lock(&pgdat->lru_lock) after them.
>
> You call that narrowing the lru locking, okay, but I see it as also
> pushing the page cache locking outwards: before this patch, page cache
> lock was taken inside lru_lock; after this patch, page cache lock is
> taken outside lru_lock. If you cannot see that, then I think you
> should not have touched this code at all; but it's what we have
> been testing, and I think we should go forward with it.
>
>>> But I wish you could give some reason for it in the commit message!
>>
>> It's a head scratch task. Would you like to tell me what's detailed info
>> should be there? Thanks!
>
> So, you don't know why you did it either: then it will be hard to
> justify. I guess I'll have to write something for it later. I'm
> strongly tempted just to drop the patch, but expect it will become
> useful later, for using lock_page_memcg() before getting lru_lock.
>
I thought the xa_lock and lru_lock relationship was described clear
in the commit log, and still no idea of the move_lock in the chain.
Please refill them for what I overlooked.
Thanks!
>>> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
>>> Is that correct? Or Wei Yang suggested some part of it perhaps?
>>
>> Yes, we talked a lot to confirm the locking change is safe.
>
> Okay, but the patch was written by you, and sent by you to Andrew:
> that is not a case for "Signed-off-by: Someone Else".
>
Ok. let's remove his signed-off.
>>> [PATCH v18 27/32] mm/swap.c: optimizing __pagevec_lru_add lru_lock
>>> Could we please drop this one for the moment? And come back to it later
>>> when the basic series is safely in. It's a good idea to try sorting
>>> together those pages which come under the same lock (though my guess is
>>> that they naturally gather themselves together quite well already); but
>>> I'm not happy adding 360 bytes to the kernel stack here (and that in
>>> addition to 192 bytes of horrid pseudo-vma in the shmem swapin case),
>>> though that could be avoided by making it per-cpu. But I hope there's
>>> a simpler way of doing it, as efficient, but also useful for the other
>>> pagevec operations here: perhaps scanning the pagevec for same page->
>>> mem_cgroup (and flags node bits), NULLing entries as they are done.
>>> Another, easily fixed, minor defect in this patch: if I'm reading it
>>> right, it reverses the order in which the pages are put on the lru?
>>
>> this patch could give about 10+% performance gain on my multiple memcg
>> readtwice testing. fairness locking cost the performance much.
>
> Good to know, should have been mentioned. s/fairness/Repeated/
>
> But what was the gain or loss on your multiple memcg readtwice
> testing without this patch, compared against node-only lru_lock?
> The 80% gain mentioned before, I presume. So this further
> optimization can wait until the rest is solid.
the gain based on the patch 26.
>
>>
>> I also tried per cpu solution but that cause much trouble of per cpu func
>> things, and looks no benefit except a bit struct size of stack, so if
>> stack size still fine. May we could use the solution and improve it better.
>> like, functionlize, fix the reverse issue etc.
>
> I don't know how important the stack depth consideration is nowadays:
> I still care, maybe others don't, since VMAP_STACK became an option.
>
> Yes, please fix the reversal (if I was right on that); and I expect
> you could use a singly linked list instead of the double.
single linked list is more saving, but do we have to reverse walking to seek
the head or tail for correct sequence?
>
> But I'll look for an alternative - later, once the urgent stuff
> is completed - and leave the acks on this patch to others.
Ok, looking forward for your new solution!
Thanks
Alex
next prev parent reply other threads:[~2020-09-11 2:52 UTC|newest]
Thread overview: 102+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-24 12:54 [PATCH v18 00/32] per memcg lru_lock Alex Shi
2020-08-24 12:54 ` [PATCH v18 01/32] mm/memcg: warning on !memcg after readahead page charged Alex Shi
2020-08-24 12:54 ` [PATCH v18 02/32] mm/memcg: bail out early from swap accounting when memcg is disabled Alex Shi
2020-08-24 12:54 ` [PATCH v18 03/32] mm/thp: move lru_add_page_tail func to huge_memory.c Alex Shi
2020-08-24 12:54 ` [PATCH v18 04/32] mm/thp: clean up lru_add_page_tail Alex Shi
2020-08-24 12:54 ` [PATCH v18 05/32] mm/thp: remove code path which never got into Alex Shi
2020-08-24 12:54 ` [PATCH v18 06/32] mm/thp: narrow lru locking Alex Shi
2020-09-10 13:49 ` Matthew Wilcox
2020-09-11 3:37 ` Alex Shi
2020-09-13 15:27 ` Matthew Wilcox
2020-09-19 1:00 ` Hugh Dickins
2020-08-24 12:54 ` [PATCH v18 07/32] mm/swap.c: stop deactivate_file_page if page not on lru Alex Shi
2020-08-24 12:54 ` [PATCH v18 08/32] mm/vmscan: remove unnecessary lruvec adding Alex Shi
2020-08-24 12:54 ` [PATCH v18 09/32] mm/page_idle: no unlikely double check for idle page counting Alex Shi
2020-08-24 12:54 ` [PATCH v18 10/32] mm/compaction: rename compact_deferred as compact_should_defer Alex Shi
2020-08-24 12:54 ` [PATCH v18 11/32] mm/memcg: add debug checking in lock_page_memcg Alex Shi
2020-08-24 12:54 ` [PATCH v18 12/32] mm/memcg: optimize mem_cgroup_page_lruvec Alex Shi
2020-08-24 12:54 ` [PATCH v18 13/32] mm/swap.c: fold vm event PGROTATED into pagevec_move_tail_fn Alex Shi
2020-08-24 12:54 ` [PATCH v18 14/32] mm/lru: move lru_lock holding in func lru_note_cost_page Alex Shi
2020-08-24 12:54 ` [PATCH v18 15/32] mm/lru: move lock into lru_note_cost Alex Shi
2020-09-21 21:36 ` Hugh Dickins
2020-09-21 22:03 ` Hugh Dickins
2020-09-22 3:39 ` Alex Shi
2020-09-22 3:38 ` Alex Shi
2020-08-24 12:54 ` [PATCH v18 16/32] mm/lru: introduce TestClearPageLRU Alex Shi
2020-09-21 23:16 ` Hugh Dickins
2020-09-22 3:53 ` Alex Shi
2020-08-24 12:54 ` [PATCH v18 17/32] mm/compaction: do page isolation first in compaction Alex Shi
2020-09-21 23:49 ` Hugh Dickins
2020-09-22 4:57 ` Alex Shi
2020-08-24 12:54 ` [PATCH v18 18/32] mm/thp: add tail pages into lru anyway in split_huge_page() Alex Shi
2020-08-24 12:54 ` [PATCH v18 19/32] mm/swap.c: serialize memcg changes in pagevec_lru_move_fn Alex Shi
2020-09-22 0:42 ` Hugh Dickins
2020-09-22 5:00 ` Alex Shi
2020-08-24 12:54 ` [PATCH v18 20/32] mm/lru: replace pgdat lru_lock with lruvec lock Alex Shi
2020-09-22 5:27 ` Hugh Dickins
2020-09-22 8:58 ` Alex Shi
2020-08-24 12:54 ` [PATCH v18 21/32] mm/lru: introduce the relock_page_lruvec function Alex Shi
2020-09-22 5:40 ` Hugh Dickins
2020-08-24 12:54 ` [PATCH v18 22/32] mm/vmscan: use relock for move_pages_to_lru Alex Shi
2020-09-22 5:44 ` Hugh Dickins
2020-09-23 1:55 ` Alex Shi
2020-08-24 12:54 ` [PATCH v18 23/32] mm/lru: revise the comments of lru_lock Alex Shi
2020-09-22 5:48 ` Hugh Dickins
2020-08-24 12:54 ` [PATCH v18 24/32] mm/pgdat: remove pgdat lru_lock Alex Shi
2020-09-22 5:53 ` Hugh Dickins
2020-09-23 1:55 ` Alex Shi
2020-08-24 12:54 ` [PATCH v18 25/32] mm/mlock: remove lru_lock on TestClearPageMlocked in munlock_vma_page Alex Shi
2020-08-26 5:52 ` Alex Shi
2020-09-22 6:13 ` Hugh Dickins
2020-09-23 1:58 ` Alex Shi
2020-08-24 12:54 ` [PATCH v18 26/32] mm/mlock: remove __munlock_isolate_lru_page Alex Shi
2020-08-24 12:55 ` [PATCH v18 27/32] mm/swap.c: optimizing __pagevec_lru_add lru_lock Alex Shi
2020-08-26 9:07 ` Alex Shi
2020-08-24 12:55 ` [PATCH v18 28/32] mm/compaction: Drop locked from isolate_migratepages_block Alex Shi
2020-08-24 12:55 ` [PATCH v18 29/32] mm: Identify compound pages sooner in isolate_migratepages_block Alex Shi
2020-08-24 12:55 ` [PATCH v18 30/32] mm: Drop use of test_and_set_skip in favor of just setting skip Alex Shi
2020-08-24 12:55 ` [PATCH v18 31/32] mm: Add explicit page decrement in exception path for isolate_lru_pages Alex Shi
2020-09-09 1:01 ` Matthew Wilcox
2020-09-09 15:43 ` Alexander Duyck
2020-09-09 17:07 ` Matthew Wilcox
2020-09-09 18:24 ` Hugh Dickins
2020-09-09 20:15 ` Matthew Wilcox
2020-09-09 21:05 ` Hugh Dickins
2020-09-09 21:17 ` Alexander Duyck
2020-08-24 12:55 ` [PATCH v18 32/32] mm: Split release_pages work into 3 passes Alex Shi
2020-08-24 18:42 ` [PATCH v18 00/32] per memcg lru_lock Andrew Morton
2020-08-24 20:24 ` Hugh Dickins
2020-08-25 1:56 ` Daniel Jordan
2020-08-25 3:26 ` Alex Shi
2020-08-25 11:39 ` Matthew Wilcox
2020-08-26 1:19 ` Daniel Jordan
2020-08-26 8:59 ` Alex Shi
2020-08-28 1:40 ` Daniel Jordan
2020-08-28 5:22 ` Alex Shi
2020-09-09 2:44 ` Aaron Lu
2020-09-09 11:40 ` Michal Hocko
2020-08-25 8:52 ` Alex Shi
2020-08-25 13:00 ` Alex Shi
2020-08-27 7:01 ` Hugh Dickins
2020-08-27 12:20 ` Race between freeing and waking page Matthew Wilcox
2020-09-08 23:41 ` [PATCH v18 00/32] per memcg lru_lock: reviews Hugh Dickins
2020-09-09 2:24 ` Wei Yang
2020-09-09 15:08 ` Alex Shi
2020-09-09 23:16 ` Hugh Dickins
2020-09-11 2:50 ` Alex Shi [this message]
2020-09-12 2:13 ` Hugh Dickins
2020-09-13 14:21 ` Alex Shi
2020-09-15 8:21 ` Hugh Dickins
2020-09-15 16:58 ` Daniel Jordan
2020-09-16 12:44 ` Alex Shi
2020-09-17 2:37 ` Alex Shi
2020-09-17 14:35 ` Daniel Jordan
2020-09-17 15:39 ` Alexander Duyck
2020-09-17 16:48 ` Daniel Jordan
2020-09-12 8:38 ` Hugh Dickins
2020-09-13 14:22 ` Alex Shi
2020-09-09 16:11 ` Alexander Duyck
2020-09-10 0:32 ` Hugh Dickins
2020-09-10 14:24 ` Alexander Duyck
2020-09-12 5:12 ` Hugh Dickins
2020-08-25 7:21 ` [PATCH v18 00/32] per memcg lru_lock Michal Hocko
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