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Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1sZxyT-00000001Lru-38NA; Fri, 02 Aug 2024 19:30:01 +0000 Date: Fri, 2 Aug 2024 20:30:01 +0100 From: Matthew Wilcox To: alexs@kernel.org Cc: Vitaly Wool , Miaohe Lin , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, minchan@kernel.org, senozhatsky@chromium.org, david@redhat.com, 42.hyeyoo@gmail.com, Yosry Ahmed , nphamcs@gmail.com Subject: Re: [PATCH v4 01/22] mm/zsmalloc: add zpdesc memory descriptor for zswap.zpool Message-ID: References: <20240729112534.3416707-1-alexs@kernel.org> <20240729112534.3416707-2-alexs@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240729112534.3416707-2-alexs@kernel.org> X-Rspam-User: X-Stat-Signature: ijqoxuiyqwcky4ng18hqyrwttr7mptts X-Rspamd-Queue-Id: 7ACCF40002 X-Rspamd-Server: rspam11 X-HE-Tag: 1722627010-483470 X-HE-Meta: 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 PBV1lnNf pmFfbnfdsi2HOmQXf7ZKOn/noRyP14PVTYL+Y60K1HGANwO/b6acCLSojMMp+8Ax4/dAk+uTzpWq0MNZHlX1rpb8INe+9Yi/sNYUlSwUdsneyZF8HQHd32zidmeO7hU6W0EmiXa1qRlEIxNhQcRyshVF1IrutLPz0vlWnkAkKZ4jPe5BCofLnPfp6n8CWqsWVWhXDFCV/VTAwtfSA8OUEf8DZwLxnRcbdKywyAWzSPaaoMxDNqk11xZN3LS4+cEXeabgTB/Waowj7HITt+KC1bnPXyUNCbmIlY+G31BdDWOsA/o4Ev+jq1x2/W2qtwgx/pis7bTkUEIh5Ct86o5wl8rYY3g== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Jul 29, 2024 at 07:25:13PM +0800, alexs@kernel.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; }; 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 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.