linux-kernel - Re: [PATCH v3 1/2] mm/zswap: global lru and shrinker shared by all zswap

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Date: Tue, 20 Feb 2024 11:24:03 +0800
From: Chengming Zhou <zhouchengming@...edance.com>
To: Nhat Pham <nphamcs@...il.com>
Cc: Johannes Weiner <hannes@...xchg.org>, Yosry Ahmed
 <yosryahmed@...gle.com>, Andrew Morton <akpm@...ux-foundation.org>,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] mm/zswap: global lru and shrinker shared by all
 zswap_pools

On 2024/2/20 09:28, Nhat Pham wrote:
> On Fri, Feb 16, 2024 at 12:55 AM Chengming Zhou
> <zhouchengming@...edance.com> wrote:
>>
>> Dynamic zswap_pool creation may create/reuse to have multiple
>> zswap_pools in a list, only the first will be current used.
>>
>> Each zswap_pool has its own lru and shrinker, which is not
>> necessary and has its problem:
>>
>> 1. When memory has pressure, all shrinker of zswap_pools will
>>    try to shrink its own lru, there is no order between them.
>>
>> 2. When zswap limit hit, only the last zswap_pool's shrink_work
>>    will try to shrink its lru list. The rationale here was to
>>    try and empty the old pool first so that we can completely
>>    drop it. However, since we only support exclusive loads now,
>>    the LRU ordering should be entirely decided by the order of
>>    stores, so the oldest entries on the LRU will naturally be
>>    from the oldest pool.
>>
>> Anyway, having a global lru and shrinker shared by all zswap_pools
>> is better and efficient.
>>
>> Acked-by: Yosry Ahmed <yosryahmed@...gle.com>
>> Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
>> ---
>>  mm/zswap.c | 171 ++++++++++++++++++++++++-------------------------------------
>>  1 file changed, 66 insertions(+), 105 deletions(-)
>>
>> diff --git a/mm/zswap.c b/mm/zswap.c
>> index 62fe307521c9..d275eb523fc4 100644
>> --- a/mm/zswap.c
>> +++ b/mm/zswap.c
>> @@ -176,14 +176,19 @@ struct zswap_pool {
>>         struct kref kref;
>>         struct list_head list;
>>         struct work_struct release_work;
>> -       struct work_struct shrink_work;
>>         struct hlist_node node;
>>         char tfm_name[CRYPTO_MAX_ALG_NAME];
>> +};
>> +
>> +static struct {
>>         struct list_lru list_lru;
>> -       struct mem_cgroup *next_shrink;
>> -       struct shrinker *shrinker;
>>         atomic_t nr_stored;
>> -};
>> +       struct shrinker *shrinker;
>> +       struct work_struct shrink_work;
>> +       struct mem_cgroup *next_shrink;
>> +       /* The lock protects next_shrink. */
>> +       spinlock_t shrink_lock;
>> +} zswap;
> 
> nit: Is there a reason why we're putting these in a struct instead of
> just a bunch of static variables (perhaps prefixed with zswap?)

No reason, both is ok for me. I thought there should be no difference.
But I can change to static variables if it's preferred in kernel. :)