On Tue, 26 Feb 2019, Jason A. Harmening wrote:
...
Log:
FFS: allow sendfile(2) to work with block sizes greater than the page size
Implement ffs_getpages_async(), which when possible calls the asynchronous
flavor of the generic pager's getpages function. When the underlying
block size is larger than the system page size, however, it will invoke
the (synchronous) buffer cache pager, followed by a call to the client
completion routine. This retains true asynchronous completion in the most
common (block size <= page size) case, which is important for the performance
of the new sendfile(2). The behavior in the larger block size case mirrors
the default implementation of VOP_GETPAGES_ASYNC, which most other
filesystems use anyway as they do not override the getpages_async method.
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.
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
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