From: Sergey Senozhatsky <senozhatsky@chromium.org>
To: Yosry Ahmed <yosryahmed@google.com>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>,
Yu Zhao <yuzhao@google.com>, Minchan Kim <minchan@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCHv4 0/4] zsmalloc: fine-grained fullness and new compaction algorithm
Date: Mon, 17 Apr 2023 20:12:43 +0900 [thread overview]
Message-ID: <20230417111243.GN25053@google.com> (raw)
In-Reply-To: <CAJD7tkZFufCacfu-EeqwhQBYXt8dpea1DYhyDgponjFjdLt5Sw@mail.gmail.com>
On (23/04/17 01:29), Yosry Ahmed wrote:
> > @@ -2239,8 +2241,8 @@ static unsigned long __zs_compact(struct zs_pool *pool,
> > if (fg == ZS_INUSE_RATIO_0) {
> > free_zspage(pool, class, src_zspage);
> > pages_freed += class->pages_per_zspage;
> > - src_zspage = NULL;
> > }
> > + src_zspage = NULL;
> >
> > if (get_fullness_group(class, dst_zspage) == ZS_INUSE_RATIO_100
> > || spin_is_contended(&pool->lock)) {
>
> For my own education, how can this result in the "next is NULL" debug
> error Yu Zhao is seeing?
>
> IIUC if we do not set src_zspage to NULL properly after putback, then
> we will attempt to putback again after the main loop in some cases.
> This can result in a zspage being present more than once in the
> per-class fullness list, right?
>
> I am not sure how this can lead to "next is NULL", which sounds like a
> corrupted list_head, because the next ptr should never be NULL as far
> as I can tell. I feel like I am missing something.
That's a good question to which I don't have an answer. We can list_add()
the same zspage twice, unlocking the pool after first list_add() so that
another process (including another zs_compact()) can do something to that
zspage. The answer is somewhere between these lines, I guess.
I can see how, for example, another DEBUG_LIST check can be triggered:
"list_add double add", because we basically can do
list_add(page, list)
list_add(page, list)
I can also see how lockdep can be unhappy with us doing
write_unlock(&zspage->lock);
write_unlock(&zspage->lock);
But I don't think I see how "next is NULL" happens (I haven't observed
it).
next prev parent reply other threads:[~2023-04-17 11:14 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-04 3:48 [PATCHv4 0/4] zsmalloc: fine-grained fullness and new compaction algorithm Sergey Senozhatsky
2023-03-04 3:48 ` [PATCHv4 1/4] zsmalloc: remove insert_zspage() ->inuse optimization Sergey Senozhatsky
2023-03-04 3:48 ` [PATCHv4 2/4] zsmalloc: fine-grained inuse ratio based fullness grouping Sergey Senozhatsky
2023-03-04 3:48 ` [PATCHv4 3/4] zsmalloc: rework compaction algorithm Sergey Senozhatsky
2023-04-17 5:01 ` [PATCH] zsmalloc: reset compaction source zspage pointer after putback_zspage() Sergey Senozhatsky
2023-04-17 5:11 ` Yu Zhao
2023-04-17 11:43 ` Yosry Ahmed
2023-04-17 13:07 ` Sergey Senozhatsky
2023-04-17 13:08 ` Sergey Senozhatsky
2023-03-04 3:48 ` [PATCHv4 4/4] zsmalloc: show per fullness group class stats Sergey Senozhatsky
2023-03-10 21:10 ` [PATCHv4 0/4] zsmalloc: fine-grained fullness and new compaction algorithm Minchan Kim
2023-03-11 8:30 ` Sergey Senozhatsky
2023-04-16 7:20 ` Yu Zhao
2023-04-16 15:18 ` Sergey Senozhatsky
2023-04-16 19:27 ` Yu Zhao
2023-04-17 2:44 ` Sergey Senozhatsky
2023-04-17 2:55 ` Yu Zhao
2023-04-17 3:52 ` Sergey Senozhatsky
2023-04-17 8:29 ` Yosry Ahmed
2023-04-17 11:12 ` Sergey Senozhatsky [this message]
2023-04-17 11:16 ` Yosry Ahmed
2023-04-17 11:24 ` Sergey Senozhatsky
2023-04-17 11:31 ` Yosry Ahmed
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