linux-kernel - Re: [PATCH 2/2] mm/zswap: split zswap rb-tree

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Date: Fri, 19 Jan 2024 14:20:51 +0800
From: Chengming Zhou <zhouchengming@...edance.com>
To: Johannes Weiner <hannes@...xchg.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 Yosry Ahmed <yosryahmed@...gle.com>, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, Chris Li <chriscli@...gle.com>,
 Nhat Pham <nphamcs@...il.com>
Subject: Re: [PATCH 2/2] mm/zswap: split zswap rb-tree

On 2024/1/18 23:11, Johannes Weiner wrote:
> On Wed, Jan 17, 2024 at 09:23:19AM +0000, Chengming Zhou wrote:
>> Each swapfile has one rb-tree to search the mapping of swp_entry_t to
>> zswap_entry, that use a spinlock to protect, which can cause heavy lock
>> contention if multiple tasks zswap_store/load concurrently.
>>
>> Optimize the scalability problem by splitting the zswap rb-tree into
>> multiple rb-trees, each corresponds to SWAP_ADDRESS_SPACE_PAGES (64M),
>> just like we did in the swap cache address_space splitting.
>>
>> Although this method can't solve the spinlock contention completely, it
>> can mitigate much of that contention. Below is the results of kernel build
>> in tmpfs with zswap shrinker enabled:
>>
>>      linux-next  zswap-lock-optimize
>> real 1m9.181s    1m3.820s
>> user 17m44.036s  17m40.100s
>> sys  7m37.297s   4m54.622s
>>
>> So there are clearly improvements.
>>
>> Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
> 
> Acked-by: Johannes Weiner <hannes@...xchg.org>
> 
> One minor nit:
> 
>> @@ -265,6 +266,10 @@ static bool zswap_has_pool;
>>  * helpers and fwd declarations
>>  **********************************/
>>  
>> +#define swap_zswap_tree(entry)					\
>> +	(&zswap_trees[swp_type(entry)][swp_offset(entry)	\
>> +		>> SWAP_ADDRESS_SPACE_SHIFT])
> 
> Make this a static inline function instead?

Good suggestion, will do.

Thanks.