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Message-ID: <ce81ab97-985b-49b8-9c84-5a3f59701f0c@bytedance.com>
Date: Fri, 2 Feb 2024 21:00:48 +0800
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Subject: Re: [PATCH 6/6] mm/zswap: zswap entry doesn't need refcount anymore
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To: Yosry Ahmed <yosryahmed@google.com>
Cc: Nhat Pham <nphamcs@gmail.com>, Johannes Weiner <hannes@cmpxchg.org>,
 Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org,
 linux-mm@kvack.org
References: <20240201-b4-zswap-invalidate-entry-v1-0-56ed496b6e55@bytedance.com>
 <20240201-b4-zswap-invalidate-entry-v1-6-56ed496b6e55@bytedance.com>
 <ZbxBT98Ctjvd0XPG@google.com>
From: Chengming Zhou <zhouchengming@bytedance.com>
In-Reply-To: <ZbxBT98Ctjvd0XPG@google.com>
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On 2024/2/2 09:11, Yosry Ahmed wrote:
> On Thu, Feb 01, 2024 at 03:49:06PM +0000, Chengming Zhou wrote:
>> Since we don't need to leave zswap entry on the zswap tree anymore,
>> we should remove it from tree once we find it from the tree.
>>
>> Then after using it, we can directly free it, no concurrent path
>> can find it from tree. Only the shrinker can see it from lru list,
>> which will also double check under tree lock, so no race problem.
>>
>> So we don't need refcount in zswap entry anymore and don't need to
>> take the spinlock for the second time to invalidate it.
>>
>> The side effect is that zswap_entry_free() maybe not happen in tree
>> spinlock, but it's ok since nothing need to be protected by the lock.
>>
>> Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
> 
> This looks like a great simplification, and a good motivation to only
> support exclusive loads. Everything is more straightforward because
> every tree lookup implies a removal and exclusive ownership.

Right, much simpler!

> 
> Let's see if removing support for non-exclusive loads is agreeable first
> though :)

Ok, I have just posted some testing data for discussion.

Thanks.