From: Matthew Wilcox <willy@infradead.org>
To: Yosry Ahmed <yosryahmed@google.com>
Cc: Kairui Song <ryncsn@gmail.com>,
linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Nhat Pham <nphamcs@gmail.com>,
Chengming Zhou <chengming.zhou@linux.dev>,
Chris Li <chrisl@kernel.org>, Barry Song <v-songbaohua@oppo.com>,
"Huang, Ying" <ying.huang@intel.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm, zswap: don't touch the XArray lock if there is no entry to free
Date: Fri, 18 Oct 2024 22:38:18 +0100 [thread overview]
Message-ID: <ZxLVSkEr_Zd2Ai3Q@casper.infradead.org> (raw)
In-Reply-To: <CAJD7tkaycBYvtTCoGsuNUekSDNnE5SZb-XyS5a8j83JsKQw4FQ@mail.gmail.com>
On Fri, Oct 18, 2024 at 02:00:16PM -0700, Yosry Ahmed wrote:
> On Fri, Oct 18, 2024 at 1:55 PM Matthew Wilcox <willy@infradead.org> wrote:
> >
> > On Fri, Oct 18, 2024 at 01:40:18PM -0700, Yosry Ahmed wrote:
> > > Oh I thought xas_reload() is enough here to check that the entry is
> > > still there after the lock is acquired. Do we have to start the walk
> > > over after holding the lock?
> >
> > Yes. The entry is guaranteed to still be valid, but the node you're
> > looking in might have been freed, so you can't modify the node without
> > making sure the node is still in the tree. We could make that cheaper
> > than a rewalk, but you're going to need to write that code since you're
> > the first to want to do something like this.
>
> I see, thanks for elaborating.
>
> Could you confirm if the current patch with the xas_reset() added
> would be equivalent to just checking xa_load() before using
> xa_erase()?
Yes, I think it would, so it's probably a poor tradeoff.
next prev parent reply other threads:[~2024-10-18 21:38 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-10-18 19:25 Kairui Song
2024-10-18 19:46 ` Matthew Wilcox
2024-10-18 20:01 ` Kairui Song
2024-10-18 20:40 ` Yosry Ahmed
2024-10-18 20:55 ` Matthew Wilcox
2024-10-18 21:00 ` Yosry Ahmed
2024-10-18 21:38 ` Matthew Wilcox [this message]
2024-10-18 22:28 ` Yosry Ahmed
2024-10-18 22:38 ` Johannes Weiner
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