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Tue, 10 Nov 2026 20:45:55 -0800 (PST) Received: from google.com ([2a00:79e0:2031:6:ad6a:b446:df00:78dc]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3b17db85a9bsm2707226a91.14.2026.11.10.20.45.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 10 Nov 2026 20:45:54 -0800 (PST) Date: Wed, 11 Nov 2026 13:45:51 +0900 From: Sergey Senozhatsky To: Nhat Pham Cc: Sergey Senozhatsky , Andrew Morton , Yosry Ahmed , Johannes Weiner , Brian Geffon , Minchan Kim , Richard Chang , linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v2 08/11] zsmalloc: encode 1-based obj_idx so valid obj is never 0 Message-ID: References: <20261110054836.1515030-1-senozhatsky@chromium.org> <20261110054836.1515030-9-senozhatsky@chromium.org> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On (26/11/10 10:57), Nhat Pham wrote: > > The next patch embeds struct zs_handle into zram and zswap entries, > > and a handle is considered allocated when its obj is not 0. But obj > > can be 0: object 0 of a zspage whose first page is PFN 0 encodes to > > 0, and some platforms do give PFN 0 to the page allocator. > > > > Store obj_idx + 1 in obj, so that a valid obj is never 0, and adjust > > ZS_MIN_ALLOC_SIZE so that the largest index still fits. Unlike a > > separate tag bit, this doesn't take any bits from obj. zsmalloc did > > the same before handles moved to handle_cachep, see > > commit 67296874eb1c ("staging: zsmalloc: Ensure handle is never 0 on > > success"). > > > > Signed-off-by: Sergey Senozhatsky > > Bit convoluted, I assume the this is so that we can use obj's 0 value > to mark unallocated state? Correct, 0 is for zs_handle_is_allocated().