Date: Thu, 4 Oct 2012 23:51:09 +0400 From: Sergey Kandaurov <pluknet@gmail.com> To: Darrel <levitch@iglou.com> Cc: current@freebsd.org Subject: Re: memory warnings r240891 | dmesgg Message-ID: <CAE-mSOJUYCtzEQZzj2gm=fBUsqA8EsXA99fzp7KQe-=urc0Lbg@mail.gmail.com> In-Reply-To: <alpine.GSO.2.00.1210041212060.1991@shell1> References: <alpine.GSO.2.00.1210041212060.1991@shell1>
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On 4 October 2012 20:18, Darrel <levitch@iglou.com> wrote: > Hello, > > Swap was created twice on this 9.0 release candidate install- once as > part of zfs and also as encrypted hard drive space. > > (30) @ 12:01:50> swapinfo > Device 1K-blocks Used Avail Capacity > /dev/zvol/bigD/swap 4194304 0 4194304 0% > /dev/gpt/swap0.eli 3145728 0 3145728 0% > /dev/gpt/swap1.eli 3145728 0 3145728 0% > Total 10485760 0 10485760 0% [...] > ************************************************************* > FreeBSD 10.0-CURRENT #1 r240891: Tue Sep 25 00:51:03 EDT 2012 > [...] > real memory = 1073741824 (1024 MB) > avail memory = 937144320 (893 MB [...] > > warning: total configured swap (2621440 pages) exceeds maximum > recommended amount (1852656 pages). > > warning: increase kern.maxswzone or reduce amount of swap. > > ************************************************************* > > Apparently kern.maxswzone is currently equal to 0. How might I tweak it > just enough to fix this? So, reduce amount of swap :) This is because kernel needs some memory to manage swap too. Currently for amd64 this roughly reduces to the following rule (My apologies in advance for the extra simplification): 100MB RAM per 800MB swap space. So, with your current amount of RAM (893MB) it is recommended to setup no more than 7144 MB of swap. [1] [1] Let's look at vm/swap_pager.c:swapon_check_swzone(npages). Here npages is the total swap pages you want to setup. The warning will trigger if (npages > maxpages / 2) becomes true. maxpages is the maximum pages the system can use for swap management. It is calculated as: maxpages = uma_zone_get_max(swap_zone) * SWAP_META_PAGES; By default SWAP_META_PAGES is 32 on amd64, and swap_zone limit calculates as available memory pages in system divided by two (assuming that maxswzone is zero (by default on amd64) and cannot further affect the limit). So that with X total pages in system, the maximum Y swap pages you are advised to have is: Y = X * SWAP_META_PAGES / 2 / 2, or X * 8 (on amd64). -- wbr, pluknet
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