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Subject: Re: UFS: unaligned read from GELI with 8k sectorsize
To: Konstantin Belousov <kostikbel@gmail.com>
References: <f84b069b-aeee-ff3c-d4f9-e2fe3caaddb1@citrin.ru>
 <20161001114536.GX38409@kib.kiev.ua>
Cc: "freebsd-fs@freebsd.org" <freebsd-fs@freebsd.org>
From: Anton Yuzhaninov <citrin@citrin.ru>
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Date: Sat, 1 Oct 2016 15:51:38 -0400
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On 2016-10-01 07:45, Konstantin Belousov wrote:
> On Sat, Oct 01, 2016 at 12:42:09AM -0400, Anton Yuzhaninov wrote:
> FreeBSD vnode pager assumes that it can read at page granularity.
> Since x86 page size is 4k, sometimes page-in has to occur not on the
> fragment boundary.  In other words, fragment size > 4k are effectively
> not supported.

You mean that geom sector size > 4k is not supported?

UFS with 8k fragment should work (over geom provider with sector size <= 
4k).

> Boot needs to execute files from the root mount, which results in the
> mmap(2) attempts on your file system.  While mount and reads/writes do
> not involve the pager, which does not trigger further bugs in the
> buffer cache code.  It should break if you try to execute badly aligned
> ELF binary from your stick, or just mmap() a file from the stick with
> non-8k aligned offset.

Thank you for detailed answer!