Date: 12 May 2018 12:46:13 -0400 From: "John Levine" <johnl@iecc.com> To: freebsd-questions@freebsd.org Cc: gobble.wa@gmail.com Subject: Re: swapfile question Message-ID: <20180512164613.AD3372675650@ary.qy> In-Reply-To: <CAFuo_fxUspphdS3eiX99gzkesDxuZw%2BVbxHbfZj7phEPvr-C_w@mail.gmail.com>
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In article <CAFuo_fxUspphdS3eiX99gzkesDxuZw+VbxHbfZj7phEPvr-C_w@mail.gmail.com> you write: >On Sat, May 12, 2018 at 6:51 AM, tech-lists <tech-lists@zyxst.net> wrote: >> Hi, >> >> In a SSD/amd64/ufs2/freebsd-11 context, which is faster: >> >> 1. swap as a partition on the ssd >> 2. swap as a file on the ssd >> >> If one is faster than the other, why? To what extent? A partition is faster since using a swap file requires looking up block numbers using inodes and indirect blocks. In the worst case the difference could be 2:1, a block number lookup for every page, typically not that bad but it's always slower. I agree that in general it's better to set up your system so it doesn't need to swap but you always want enough swap to avoid strange program failures when malloc() calls fail. (They're supposed to recover but I can assure you, they often don't.) I have an application that answers network queries from a mysql database. The database is largish, several hundred megabytes, but only changes a few times a day. I rewrote my application so it slurps the whole database into a perl table and answers queries from that. The perl table is bigger than the VM's physical memory so it's mostly swapped out, but using the VM system for disk I/O is faster in this application than calling out to mysql. -- Regards, John Levine, johnl@iecc.com, Primary Perpetrator of "The Internet for Dummies", Please consider the environment before reading this e-mail. https://jl.ly
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