From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx181.postini.com [74.125.245.181]) by kanga.kvack.org (Postfix) with SMTP id AA5806B0071 for ; Wed, 24 Oct 2012 23:12:34 -0400 (EDT) Received: by mail-ie0-f169.google.com with SMTP id 10so2112637ied.14 for ; Wed, 24 Oct 2012 20:12:34 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20121025025826.GB23462@localhost> References: <1350996411-5425-1-git-send-email-casualfisher@gmail.com> <20121023224706.GR4291@dastard> <20121024201921.GX4291@dastard> <20121025015014.GC29378@dastard> <50889FF1.9030107@gmail.com> <20121025025826.GB23462@localhost> Date: Thu, 25 Oct 2012 11:12:33 +0800 Message-ID: Subject: Re: [PATCH] mm: readahead: remove redundant ra_pages in file_ra_state From: YingHang Zhu Content-Type: text/plain; charset=ISO-8859-1 Sender: owner-linux-mm@kvack.org List-ID: To: Fengguang Wu Cc: akpm@linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Ni zhan Chen , Dave Chinner On Thu, Oct 25, 2012 at 10:58 AM, Fengguang Wu wrote: > Hi Chen, > >> But how can bdi related ra_pages reflect different files' readahead >> window? Maybe these different files are sequential read, random read >> and so on. > > It's simple: sequential reads will get ra_pages readahead size while > random reads will not get readahead at all. > > Talking about the below chunk, it might hurt someone that explicitly > takes advantage of the behavior, however the ra_pages*2 seems more > like a hack than general solution to me: if the user will need > POSIX_FADV_SEQUENTIAL to double the max readahead window size for > improving IO performance, then why not just increase bdi->ra_pages and > benefit all reads? One may argue that it offers some differential > behavior to specific applications, however it may also present as a > counter-optimization: if the root already tuned bdi->ra_pages to the > optimal size, the doubled readahead size will only cost more memory > and perhaps IO latency. I agree, we should choose the reasonable solution here. Thanks, Ying Zhu > > --- a/mm/fadvise.c > +++ b/mm/fadvise.c > @@ -87,7 +86,6 @@ SYSCALL_DEFINE(fadvise64_64)(int fd, loff_t offset, loff_t len, int advice) > spin_unlock(&file->f_lock); > break; > case POSIX_FADV_SEQUENTIAL: > - file->f_ra.ra_pages = bdi->ra_pages * 2; > spin_lock(&file->f_lock); > file->f_mode &= ~FMODE_RANDOM; > spin_unlock(&file->f_lock); > > Thanks, > Fengguang -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org