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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 694B2C6FA82 for ; Tue, 13 Sep 2022 02:10:07 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 07E556B0073; Mon, 12 Sep 2022 22:10:07 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 006A68D0001; Mon, 12 Sep 2022 22:10:06 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DC2586B0075; Mon, 12 Sep 2022 22:10:06 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id C9D686B0073 for ; Mon, 12 Sep 2022 22:10:06 -0400 (EDT) Received: from smtpin21.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 9B398140540 for ; Tue, 13 Sep 2022 02:10:06 +0000 (UTC) X-FDA: 79905432012.21.DEDC462 Received: from mail-pf1-f171.google.com (mail-pf1-f171.google.com [209.85.210.171]) by imf01.hostedemail.com (Postfix) with ESMTP id 41EC240092 for ; Tue, 13 Sep 2022 02:10:06 +0000 (UTC) Received: by mail-pf1-f171.google.com with SMTP id a80so1788212pfa.4 for ; Mon, 12 Sep 2022 19:10:06 -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=HbIsJbdpklXhNPcLc0RY7lmKO4fvnKXN6Gt2hfkBd9g=; b=nJa62AAc/Zix2+vehfKmnxBd7GwSz1F22pdW3BwVQlS/NW7I/NMfw2TQRRwJb1l6tM RpkeWRGIYH8CGTeNcv7eYD7+mkxRupi6teJCFazwslbcHY8Oiom2iqkYxtoqUTZMWYxZ ni3sx+52rQVmVSt8tA0UDLhYbXDKwSOVaKDSU= 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=HbIsJbdpklXhNPcLc0RY7lmKO4fvnKXN6Gt2hfkBd9g=; b=h5JebjPpww6JYqLgFwlEOijcxGAWh2a697FrxOG/BrujWKPWCK1g9Pa1YpBMUXFGlm GyFnGaqQ66Ox/p22rI6Y3Z8Fh7TGc45JH+N9hx6o5LXgB7OAGsuH2ePQI2olyKsU+gsS UX6OIrw3yUP+hs2BXjovnpci+XM5A9bo80SKWxlAC32VXMze2xWIwwskBV0UdANs7316 qUPDqz5Kik+JMqX4wpDIzC8FzaEgTQe4W2Fvko3vPSuGUiBDytw1V0RLltEy3Kr3v7uH EJbHmqOrch6lvMH6viUpTNEaj+19M+Bb1U1OjxLAU1XOITcxa2kNLpOSYgE5IVg6qLdo ySEA== X-Gm-Message-State: ACgBeo2fP9NWUjkHJNMloYGws1ZKZzm6CY6qIwCacLvlKOw7uCLm+NNP DGt5CxSllsODc/+nmaCMe2byLw== X-Google-Smtp-Source: AA6agR6PMK9kDio0o6BqLs/G4wBuRYfP6sm2eCpdKZ+8F/kRweE7t1gz66xBA09PfcrMDRLrtOFRUw== X-Received: by 2002:a05:6a00:15cb:b0:52e:6100:e7a7 with SMTP id o11-20020a056a0015cb00b0052e6100e7a7mr30377748pfu.23.1663035005290; Mon, 12 Sep 2022 19:10:05 -0700 (PDT) Received: from google.com ([240f:75:7537:3187:481a:bead:f512:e554]) by smtp.gmail.com with ESMTPSA id y22-20020aa78f36000000b0052d200c8040sm6350408pfr.211.2022.09.12.19.10.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 12 Sep 2022 19:10:04 -0700 (PDT) Date: Tue, 13 Sep 2022 11:10:00 +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: ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1663035006; a=rsa-sha256; cv=none; b=YdVOOAFbjophRAdWQZhdDLe/aRRxgHC0gE9hKqrC1oR53q41lF2LDOyTARUcRSIH4p+Z5U LFs/4pB8NvHUOYvaLTkVtGUcYrd0G/ijZ5Pi/rRZUFZ7jn602VuevLVDzetL5i9Ye4Rv97 SZduCb26M9maV3SMDgMuAucT7tsOu78= ARC-Authentication-Results: i=1; imf01.hostedemail.com; dkim=pass header.d=chromium.org header.s=google header.b=nJa62AAc; spf=pass (imf01.hostedemail.com: domain of senozhatsky@chromium.org designates 209.85.210.171 as permitted sender) smtp.mailfrom=senozhatsky@chromium.org; dmarc=pass (policy=none) header.from=chromium.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1663035006; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=HbIsJbdpklXhNPcLc0RY7lmKO4fvnKXN6Gt2hfkBd9g=; b=32+z1tUf0aIvm1VIltGP1mtykf9wN7gP+8k98wpcon800/ehfcYjTrG5qRB1qN75og2+mg ruOiIc9N1l1y4WjUWHaWQ5ui1Oz6Eb1Kjn12ZfUsSKuPaTkq0UoIshBn95CCC79BjPM6Uf 5nTjebdwlvp52clxU9lEbXAYAFqT9u4= X-Rspamd-Queue-Id: 41EC240092 Authentication-Results: imf01.hostedemail.com; dkim=pass header.d=chromium.org header.s=google header.b=nJa62AAc; spf=pass (imf01.hostedemail.com: domain of senozhatsky@chromium.org designates 209.85.210.171 as permitted sender) smtp.mailfrom=senozhatsky@chromium.org; dmarc=pass (policy=none) header.from=chromium.org X-Rspam-User: X-Rspamd-Server: rspam10 X-Stat-Signature: 9f3p3n9nntw8nycrtq6igj39yhi6trrj X-HE-Tag: 1663035006-128836 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: On (22/09/12 22:07), Brian Geffon wrote: > > 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. > > I apologize, you are correct. No worries! It's always good to double check. > Reviewed-by: Brian Geffon Thanks.