debuginfod: PR25978 - Created the prefetch fdcache

The debuginfod fdcache-prefetch logic has been observed to show some
degeneracies in operation.  Since fdcache evictions are done
frequently, and freshly prefetched archive elements are put at the
back of lru[], each eviction round can summarily nuke things that
were just prefetched .... and are just going to be prefetched again.
It would be better to have two lru lists, or being able to insert
newly prefetched entries somewhere in the middle of the list rather
than at the very very end.

https://sourceware.org/bugzilla/show_bug.cgi?id=25978

Signed-off-by: Noah Sanci <nsanci@redhat.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/doc/debuginfod.8 b/doc/debuginfod.8
index 1adf703a..d83c7cdb 100644
--- a/doc/debuginfod.8
+++ b/doc/debuginfod.8
@@ -216,6 +216,16 @@ most recently used extracted files are kept.  Grooming cleans this
 cache.
 
 .TP
+.B "\-\-fdcache\-\-prefetch\-fds=NUM"  "\-\-fdcache\-\-prefetch\-mbs=MB"
+Configure how many file descriptors (fds) and megabytes (mbs) are
+allocated to the prefetch fdcache. If unspecified, values of
+\fB\-\-prefetch\-fds\fP and \fB\-\-prefetch\-mbs\fP depend
+on concurrency of the system and on the available disk space on
+the $TMPDIR. Allocating more to the prefetch cache will improve
+performance in environments where different parts of several large
+archives are being accessed.
+
+.TP
 .B "\-\-fdcache\-mintmp=NUM"
 Configure a disk space threshold for emergency flushing of the cache.
 The filesystem holding the cache is checked periodically.  If the