Date: Fri, 29 Dec 2017 20:00:19 +0000 (UTC) From: Ian Lepore <ian@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r327356 - head/share/man/man4 Message-ID: <201712292000.vBTK0JGd093744@repo.freebsd.org>
next in thread | raw e-mail | index | archive | help
Author: ian Date: Fri Dec 29 20:00:19 2017 New Revision: 327356 URL: https://svnweb.freebsd.org/changeset/base/327356 Log: Correct a mistake and reword a couple sentences to clarify that "the value" refers to the scale value, not the kmem_arena size that results from scaling. Suggested by: alc@ Modified: head/share/man/man4/md.4 Modified: head/share/man/man4/md.4 ============================================================================== --- head/share/man/man4/md.4 Fri Dec 29 19:07:50 2017 (r327355) +++ head/share/man/man4/md.4 Fri Dec 29 20:00:19 2017 (r327356) @@ -116,19 +116,19 @@ The default value is 32, which is sufficient to map 12 .It Cd options VM_KMEM_SIZE_SCALE=<num> This configures the amount of kernel virtual address (KVA) space to dedicate to the kmem_arena map. -The value is the ratio of physical to virtual pages. +The scale value is the ratio of physical to virtual pages. The default value of 3 allocates a page of KVA for each 3 pages of physical ram in the system. The kernel and modules, including the root image, also consume KVA. The combination of a large root image and the default scaling -may preallocate so much KVA to kmem_arena that there is not enough +may preallocate so much KVA that there is not enough remaining address space to allocate kernel stacks, IO buffers, and other resources that are not part of kmem_arena. Overallocating kmem_arena space is likely to manifest as failure to launch userland processes with "cannot allocate kernel stack" messages. -Setting the value too high may result in kernel failure to allocate +Setting the scale value too high may result in kernel failure to allocate memory because kmem_arena is too small, and the failure may require significant runtime to manifest. Empirically, a value of 5 works well for a 200 MiB root image on
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?201712292000.vBTK0JGd093744>