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Date: Fri, 2 Feb 2024 11:26:35 -0500
From: Johannes Weiner <hannes@cmpxchg.org>
To: Chengming Zhou <zhouchengming@bytedance.com>
Cc: Nhat Pham <nphamcs@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Yosry Ahmed <yosryahmed@google.com>, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org
Subject: Re: [PATCH 5/6] mm/zswap: only support zswap_exclusive_loads_enabled
Message-ID: <20240202162635.GF1227330@cmpxchg.org>
References: <20240201-b4-zswap-invalidate-entry-v1-0-56ed496b6e55@bytedance.com>
 <20240201-b4-zswap-invalidate-entry-v1-5-56ed496b6e55@bytedance.com>
 <20240201181240.GE321148@cmpxchg.org>
 <d5455b43-aa22-4931-a6b3-062128f4d30f@bytedance.com>
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In-Reply-To: <d5455b43-aa22-4931-a6b3-062128f4d30f@bytedance.com>

On Fri, Feb 02, 2024 at 08:57:38PM +0800, Chengming Zhou wrote:
> On 2024/2/2 02:12, Johannes Weiner wrote:
> > Caching "swapout work" is helpful when the system is thrashing. Then
> > recently swapped in pages might get swapped out again very soon. It
> > certainly makes sense with conventional swap, because keeping a clean
> > copy on the disk saves IO work and doesn't cost any additional memory.
> > 
> > But with zswap, it's different. It saves some compression work on a
> > thrashing page. But the act of keeping compressed memory contributes
> > to a higher rate of thrashing. And that can cause IO in other places
> > like zswap writeback and file memory.
> 
> [...] A/B test kernel building in tmpfs directory, memory.max=2GB.
> (zswap writeback enabled and shrinker_enabled, one 50GB swapfile)
> 
> From the below results, exclusive mode has fewer scan and refault.
> 
>                               zswap-invalidate-entry        zswap-invalidate-entry-exclusive
> real                          63.80                         63.01                         
> user                          1063.83                       1061.32                       
> sys                           290.31                        266.15                        
>                               zswap-invalidate-entry        zswap-invalidate-entry-exclusive
> workingset_refault_anon       2383084.40                    1976397.40                    
> workingset_refault_file       44134.00                      45689.40                      
> workingset_activate_anon      837878.00                     728441.20                     
> workingset_activate_file      4710.00                       4085.20                       
> workingset_restore_anon       732622.60                     639428.40                     
> workingset_restore_file       1007.00                       926.80                        
> workingset_nodereclaim        0.00                          0.00                          
> pgscan                        14343003.40                   12409570.20                   
> pgscan_kswapd                 0.00                          0.00                          
> pgscan_direct                 14343003.40                   12409570.20                   
> pgscan_khugepaged             0.00                          0.00                         

That's perfect. Thanks!

Would you mind adding all of the above into the changelog?

With that,

Acked-by: Johannes Weiner <hannes@cmpxchg.org>