From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0DA99C6FA82 for ; Tue, 13 Sep 2022 01:54:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229691AbiIMByo (ORCPT ); Mon, 12 Sep 2022 21:54:44 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57428 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229754AbiIMByl (ORCPT ); Mon, 12 Sep 2022 21:54:41 -0400 Received: from mail-pf1-x42a.google.com (mail-pf1-x42a.google.com [IPv6:2607:f8b0:4864:20::42a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A72EDDE86 for ; Mon, 12 Sep 2022 18:54:40 -0700 (PDT) Received: by mail-pf1-x42a.google.com with SMTP id b75so5099790pfb.7 for ; Mon, 12 Sep 2022 18:54:40 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date; bh=pE3z9bD3wrpH25CppWpqm9Q7/WCYzJnth3D82Qxm1v4=; b=TwgGk/wDWHjdQyudMHLQ8VmAf25Ydi+vzLWO1bjhdunrnMX38iDLAnzo+e7LJwKYnD Ey9AIWwURLkLihWy9U0IRzWGw8Y0VCcgARIRb1PRWUF2LxFe5mSMMC3rFf7ucI6+VcUQ Hmtz0KdSopcwaIDVezJv4L6TqGINJzTnhoCUc= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date; bh=pE3z9bD3wrpH25CppWpqm9Q7/WCYzJnth3D82Qxm1v4=; b=EzUAX/hKqZofHdxiYXaqn8mdXjsExp/gfN646++GoVsb2KxrbQyHl0hTQZ9kBd+H0M VWI6Pf9ni9gAry5fqgfoiA4SoJxebV8yVFY5LInDxTU9wZcNqCfrwpbEwF1goyTCTVOK AZp3l8ShUo5jxbwuxnja5vloYf2SJj4WlPF3C+mgBL12dhdO3Is34ifqVfKOM7cr2PEH P/EBufvvC2Uq1gPneczv+9zL5vqzlBxEq8zs4bn2egGUovM8zsubgUtP7xm92xqDbQon SrKDX2PCQNf/hB6CItTf7TgPz5Oi2PL+cxY3vDEdUpRvwXduWeJUehT/nIQr/ye1NBgX tI+A== X-Gm-Message-State: ACgBeo3OkbodqeILhAz+jVI4U2dOQ/QNjp3V9neBx3tOiw7g4jqbLFxS gi5WqzH22D2mAdp5B6g30yyEJj4qJwOh7w== X-Google-Smtp-Source: AA6agR5f8dn7gcyjPhzSjCQEUKUlhpH4GmTaxdK7mM1Nm/sJBrcwdD5XM6C18yend0AUTw2lxN0DUw== X-Received: by 2002:a63:4a1e:0:b0:438:fa59:c0f3 with SMTP id x30-20020a634a1e000000b00438fa59c0f3mr7043568pga.107.1663034080220; Mon, 12 Sep 2022 18:54:40 -0700 (PDT) Received: from google.com ([240f:75:7537:3187:481a:bead:f512:e554]) by smtp.gmail.com with ESMTPSA id a2-20020a170902710200b00172f4835f60sm6718522pll.189.2022.09.12.18.54.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 12 Sep 2022 18:54:39 -0700 (PDT) Date: Tue, 13 Sep 2022 10:54:34 +0900 From: Sergey Senozhatsky To: Brian Geffon Cc: Sergey Senozhatsky , Minchan Kim , Andrew Morton , Nitin Gupta , LKML , linux-mm Subject: Re: [PATCHv2] zram: do not waste zram_table_entry flags bits Message-ID: References: <20220912152744.527438-1-senozhatsky@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (22/09/12 11:39), Brian Geffon wrote: > > zram_table_entry::flags stores object size in the lower bits and > > zram pageflags in the upper bits. However, for some reason, we > > use 24 lower bits, while maximum zram object size is PAGE_SIZE, > > which requires PAGE_SHIFT bits (up to 16 on arm64). This wastes > > 24 - PAGE_SHIFT bits that we can use for additional zram pageflags > > instead. > > > > Also add a BUILD_BUG_ON() to alert us should we run out of bits > > in zram_table_entry::flags. > > > > Signed-off-by: Sergey Senozhatsky > > --- > > drivers/block/zram/zram_drv.c | 2 ++ > > drivers/block/zram/zram_drv.h | 15 +++++++-------- > > 2 files changed, 9 insertions(+), 8 deletions(-) > > > > diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c > > index f3948abce2f7..07913bcdb5c2 100644 > > --- a/drivers/block/zram/zram_drv.c > > +++ b/drivers/block/zram/zram_drv.c > > @@ -2449,6 +2449,8 @@ static int __init zram_init(void) > > { > > int ret; > > > > + BUILD_BUG_ON(__NR_ZRAM_PAGEFLAGS > BITS_PER_LONG); > > Should this be >= BITS_PER_LONG? __NR_ZRAM_PAGEFLAGS == BITS_PER_LONG == 64 (e.g. on 64 bit host) means that the last valid zram pageflag (and __NR_ZRAM_PAGEFLAGS is not a valid pageflag) is __NR_ZRAM_PAGEFLAGS - 1, which is 63 and which is a valid BIT() offset for u64. So __NR_ZRAM_PAGEFLAGS == BITS_PER_LONG should be a valid case.