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

[Jason Harmening]

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.

> 
> ffs_getpages() already has an almost-never-used special case for small
> block sizes.  It uses vnode_pager_generic_getpages() when !use_buf_pager
> and the block_size <= PAGE_SIZE, else vfs_bio_getpages().  But
> block_size <= PAGE_SIZE is unusual, and !use_buf_pager is also unusual,
> and use_buf_pager is mostly a debugging sysctl, so little would be
> lost but using vfs_bio_getpages() unconditionally.
> 
> Bruce