svn commit: r344562 - head/sys/ufs/ffs

[Bruce Evans]

On Mon, 25 Feb 2019, Jason Harmening wrote:

> On 2/25/19 9:46 PM, Bruce Evans wrote:
>> 
>> block_size <= PAGE_SIZE is very uncommon for ffs, even on systems with 
>> large
>> pages.  MINBSIZE is 4096 in ffs (except in my version, it is 512).  The
>> default is 32768 in newfs.  I consider this excessive and only use it for
>> file systems with many files larger than 1GB, but it is the most common 
>> size.
>> It is larger than the large page size of 8192.
>
> I think this is a case of filesystem logical block size vs. media sector 
> size, right?  Here we're checking the devvp's block size, which I think 
> should correspond to the sector size.  I'd expect cases of that being
> greater than PAGE_SIZE to be uncommon, in fact geli warns when that is the 
> case.   I probably should've made that clearer in the commit message.

Yes, I missed that you are checking devvp.  ffs_getpages() also checks
devvp.

So the bug has nothing to do with file system logical (fragment) or i/o
(block) block size's, except file systems themselves won't work unless
their i/o size is a multiple of the underlying devices (sector) i/o size.

Are there physical disk with sector size > PAGE_SIZE now?  It is easy to
create virtual (md) disks with sector size > PAGE_SIZE, and this may even
be useful for avoiding the related problem of having to access large fs
blocks to do i/o to small md sectors.  I think it is best to use PAGE_SIZE
blocks in all layers and sometimes combine these into clusters.

Bruce