linux-kernel - Re: [PATCH v4 01/22] mm/zsmalloc: add zpdesc memory descriptor for zswap.zpool

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <86e97328-a784-4320-b634-c582d5a10aff@gmail.com>
Date: Mon, 5 Aug 2024 12:36:14 +0800
From: Alex Shi <seakeel@...il.com>
To: Matthew Wilcox <willy@...radead.org>, alexs@...nel.org
Cc: Vitaly Wool <vitaly.wool@...sulko.com>, Miaohe Lin
 <linmiaohe@...wei.com>, Andrew Morton <akpm@...ux-foundation.org>,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org, minchan@...nel.org,
 senozhatsky@...omium.org, david@...hat.com, 42.hyeyoo@...il.com,
 Yosry Ahmed <yosryahmed@...gle.com>, nphamcs@...il.com
Subject: Re: [PATCH v4 01/22] mm/zsmalloc: add zpdesc memory descriptor for
 zswap.zpool



On 8/3/24 3:30 AM, Matthew Wilcox wrote:
> On Mon, Jul 29, 2024 at 07:25:13PM +0800, alexs@...nel.org wrote:
>> +/*
>> + * struct zpdesc -	Memory descriptor for zpool memory, now is for zsmalloc
>> + * @flags:		Page flags, PG_private: identifies the first component page
>> + * @lru:		Indirectly used by page migration
>> + * @mops:		Used by page migration
>> + * @next:		Next zpdesc in a zspage in zsmalloc zpool
>> + * @handle:		For huge zspage in zsmalloc zpool
>> + * @zspage:		Pointer to zspage in zsmalloc
>> + * @memcg_data:		Memory Control Group data.
>> + *
>> + * This struct overlays struct page for now. Do not modify without a good
>> + * understanding of the issues.
>> + */
>> +struct zpdesc {
>> +	unsigned long flags;
>> +	struct list_head lru;
>> +	struct movable_operations *mops;
>> +	union {
>> +		/* Next zpdescs in a zspage in zsmalloc zpool */
>> +		struct zpdesc *next;
>> +		/* For huge zspage in zsmalloc zpool */
>> +		unsigned long handle;
>> +	};
>> +	struct zspage *zspage;
>> +	unsigned long _zp_pad_1;
>> +#ifdef CONFIG_MEMCG
>> +	unsigned long memcg_data;
>> +#endif
>> +};
> 
> Before we do a v5, what's the plan for a shrunk struct page?  It feels
> like a lot of what's going on here is just "because we can".  But if you
> actually had to allocate the memory, would you?
> 
> That is, if we get to
> 
> struct page {
> 	unsigned long memdesc;
> };
> 

Yes, we still have a huge gap between this target. 

> what do you put in the 60  bits of information?  Do you allocate a
> per-page struct zpdesc, and have each one pointing to a zspage?  Or do
> you extend the current contents of zspage to describe the pages allocated
> to it, and make each struct page point to the zspage?

I am not very clear the way to get there. The easy path for me, I guess, 
would move struct zpdesc members out to zspage, like 2nd way of your suggestion.

I believe you has much more idea of the ways to memdesc. 
Is there some references or detailed info which I could learn from you?

Many thanks!
Alex
 
> 
> I don't know your code, so I'm not trying to choose for you.  I'm just
> trying to make sure we're walking in the right direction.