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Date: Thu, 14 Feb 2019 10:45:19 +0200
From: Konstantin Belousov <kostikbel@gmail.com>
To: Bruce Evans <brde@optusnet.com.au>
Cc: Justin Hibbits <chmeeedalf@gmail.com>, Gleb Smirnoff <glebius@freebsd.org>,
 src-committers@freebsd.org, svn-src-all@freebsd.org,
 svn-src-head@freebsd.org
Subject: Re: svn commit: r343030 - in head/sys: cam conf dev/md dev/nvme
 fs/fuse fs/nfsclient fs/smbfs kern sys ufs/ffs vm
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On Thu, Feb 14, 2019 at 06:56:42PM +1100, Bruce Evans wrote:
> I don't understand how pbuf_preallocate() allocates for the other
> pbuf pools.  When I debugged this for clpbufs, the preallocation was
> not used.  pbuf types other than clpbufs seem to be unused in my
> configurations.  I thought that pbufs were used during initialization,
> since they end up with a nonzero FREE count, but their only use seems
> to be to preallocate them.
vnode_pager_generic_getpages() typically not used for UFS on modern
systems. Instead the buffer pager is active which does not need pbufs,
it uses real buffers coherent with the UFS buffer cache.

To get to the actual use of pbufs now you can:
- perform clustered buffer io;
- use vnode-backed md(4) (this case is still broken if md(4) is loaded
  as a module);
- cause system swapping;
- use sendfile(2).