From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AG47ELtbQw05+gdItUPNYxSqnu/uzcx4uILly6RqcvV9Y5zUgYjTr1hK97V6fbOZ2o7Gaav1zMJF ARC-Seal: i=1; a=rsa-sha256; t=1521577056; cv=none; d=google.com; s=arc-20160816; b=S/+zMFVlqVErCLirt3Ei4jOwZadQplpre3wxamvEN9ow+Bj+gmmbJzWLximsXSi6ea MOnb/wAp9268npLuPaZX/9nRPoPWiQhCe5JwnTzrry/jn1xhxaIugOQdMhG0KwMS9Gxc H21+PN21K8+WuuFzvL7vVEyDUTwfNi/nDpe1CqchHlttKXfsXMc26aJWyrvHVKwwEncH OKT6S1BiveXb7JF5L4vBoJuQJdl3NROcAsFg16C4UU/as8mSD9sP+05tuohT/7aXqTFG tWPkdo8TV8V5ivb8mC2V+kJUu6IKjKq8relk+8wtjt8JlCGMGpRbzjjdl4lReJpsN2Xh U36w== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=user-agent:in-reply-to:content-disposition:mime-version:references :message-id:subject:cc:to:from:date:arc-authentication-results; bh=B6RwOF1O1GvwZxBxx4aKn10fdudaOwfzwSFl60ngLek=; b=tKdHSO/pVZo0sa7DODjfpt74dqt2OLY7yiJ1daPMJCSXxC8jblN1lHs16pu8Yc3QwE rgC42qoPj3pIcRsv94r18A4eQ5GMWsHeiPwViEw3Vgh/J9YJU+polxCCWmM5iWPxCcIj 9lGv/HEjKE7n4tfMt1h0y+5C8AGG819v71Rbgusi0JYIqf7Qb22g/SW2tlDR2wqLKyhr eiE+ONXUOFf4agLjuIaknhIpv52JFVga6pDz/fC49bj+2KCGnK0gox7Cw1bof6R8BvxG g01e+6+mTW/x38YjtEdE5j8np6NSyGnIb+NmMHT9N/qGG2O83cZi15db1+vtGhOYRK/X FOnA== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: domain of jack@suse.cz designates 195.135.220.15 as permitted sender) smtp.mailfrom=jack@suse.cz Authentication-Results: mx.google.com; spf=pass (google.com: domain of jack@suse.cz designates 195.135.220.15 as permitted sender) smtp.mailfrom=jack@suse.cz Date: Tue, 20 Mar 2018 21:17:30 +0100 From: Jan Kara To: Wei Wang Cc: gregkh@linuxfoundation.org, Todd Poynor , Wei Wang , Andrew Morton , Dan Williams , Michal Hocko , "Kirill A. Shutemov" , Jan Kara , =?iso-8859-1?B?Suly9G1l?= Glisse , Hugh Dickins , Matthew Wilcox , Ingo Molnar , Sherry Cheung , Oliver O'Halloran , Andrey Ryabinin , Huang Ying , Dennis Zhou , Pavel Tatashin , linux-mm@kvack.org, linux-kernel@vger.kernel.org, mgorman@suse.de Subject: Re: [PATCH] mm: add config for readahead window Message-ID: <20180320201730.xvvpc4gptqrn47ba@quack2.suse.cz> References: <20180316182512.118361-1-wvw@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170421 (1.8.2) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1595119752476729321?= X-GMAIL-MSGID: =?utf-8?q?1595489184282423101?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Fri 16-03-18 18:49:08, Wei Wang wrote: > Android devices boot time benefits by bigger readahead window setting from > init. This patch will make readahead window a config so early boot can benefit > by it as well. > > > On Fri, Mar 16, 2018 at 11:25 AM Wei Wang wrote: > > From: Wei Wang > > Change VM_MAX_READAHEAD value from the default 128KB to a configurable > value. This will allow the readahead window to grow to a maximum size > bigger than 128KB during boot, which could benefit to sequential read > throughput and thus boot performance. > > Signed-off-by: Wei Wang Just for record we had VM_MAX_READAHEAD changed to 512 in all SUSE distributions for quite some years. But just recently we were re-evaluating it and we are finding less and less reasons to keep this setting to 512 - with newer storage benefits become marginal and the overhead of reading more unnecessarily in some other corner cases is visible as well (I still have somewhere reports from 0-day robot that complained to me about two performance regressions coming from increased default readahead window). So for your specific case it might make sense to increase the window when you have a control of both the HW and the kernel but in general I tend to currently agree with Linus & co. that the current default is probably fine. I don't have a strong opinion on whether your ~90ms of boot time are good enough justification for a kernel config option... Honza -- Jan Kara SUSE Labs, CR