mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
synced 2026-05-15 17:51:41 -04:00
64912122a4
The filecache lru is walked in 2 circumstances for 2 different reasons.
1/ When called from the shrinker we want to discard the first few
entries on the list, ignoring any with NFSD_FILE_REFERENCED set
because they should really be at the end of the LRU as they have been
referenced recently. So those ones are ROTATED.
2/ When called from the nfsd_file_gc() timer function we want to discard
anything that hasn't been used since before the previous call, and
mark everything else as unused at this point in time.
Using the same flag for both of these can result in some unexpected
outcomes. If the shrinker callback clears NFSD_FILE_REFERENCED then
nfsd_file_gc() will think the file hasn't been used in a while, while
really it has.
I think it is easier to reason about the behaviour if we instead have
two flags.
NFSD_FILE_REFERENCED means "this should be at the end of the LRU, please
put it there when convenient"
NFSD_FILE_RECENT means "this has been used recently - since the last
run of nfsd_file_gc()
When either caller finds an NFSD_FILE_REFERENCED entry, that entry
should be moved to the end of the LRU and the flag cleared. This can
safely happen at any time. The actual order on the lru might not be
strictly least-recently-used, but that is normal for linux lrus.
The shrinker callback can ignore the "recent" flag. If it ends up
freeing something that is "recent" that simply means that memory
pressure is sufficient to limit the acceptable cache age to less than
the nfsd_file_gc frequency.
The gc callback should primarily focus on NFSD_FILE_RECENT. It should
free everything that doesn't have this flag set, and should clear the
flag on everything else. When it clears the flag it is convenient to
clear the "REFERENCED" flag and move to the end of the LRU too.
With this, calls from the shrinker do not prematurely age files. It
will focus only on freeing those that are least recently used.
Signed-off-by: NeilBrown <neilb@suse.de>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.