lkml.org 
[lkml]   [2019]   [Feb]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [LSF/MM TOPIC] Discuss least bad options for resolving longterm-GUP usage by RDMA
One approach that may be a clean way to solve this:

1. Long term GUP usage requires the virtual mapping to the pages be fixed
for the duration of the GUP Map. There never has been a way to break
the pinnning and thus this needs to be preserved.

2. Page Cache Long term pins are not allowed since regular filesystems
depend on COW and other tricks which are incompatible with a long term
pin.

3. Filesystems that allow bypass of the page cache (like XFS / DAX) will
provide the virtual mapping when the PIN is done and DO NO OPERATIONS
on the longterm pinned range until the long term pin is removed.
Hardware may do its job (like for persistent memory) but no data
consistency on the NVDIMM medium is guaranteed until the long term pin
is removed and the filesystems regains control over the area.

4. Long term pin means that the mapped sections are an actively used part
of the file (like a filesystem write) and it cannot be truncated for
the duration of the pin. It can be thought of as if the truncate is
immediate followed by a write extending the file again. The mapping
by RDMA implies after all that remote writes can occur at anytime
within the area pinned long term.

\
 
 \ /
  Last update: 2019-02-07 17:56    [W:1.731 / U:1.368 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site