mirror of
https://github.com/torvalds/linux.git
synced 2024-11-26 14:12:06 +00:00
A mirror of the official Linux kernel repository just in case
563f40019d
By default we set DCACHE_REFERENCED and I_REFERENCED on any dentry or inode we create. This is problematic as this means that it takes two trips through the LRU for any of these objects to be reclaimed, regardless of their actual lifetime. With enough pressure from these caches we can easily evict our working set from page cache with single use objects. So instead only set *REFERENCED if we've already been added to the LRU list. This means that we've been touched since the first time we were accessed, and so more likely to need to hang out in cache. To illustrate this issue I wrote the following scripts https://github.com/josefbacik/debug-scripts/tree/master/cache-pressure on my test box. It is a single socket 4 core CPU with 16gib of RAM and I tested on an Intel 2tib NVME drive. The cache-pressure.sh script creates a new file system and creates 2 6.5gib files in order to take up 13gib of the 16gib of ram with pagecache. Then it runs a test program that reads these 2 files in a loop, and keeps track of how often it has to read bytes for each loop. On an ideal system with no pressure we should have to read 0 bytes indefinitely. The second thing this script does is start a fs_mark job that creates a ton of 0 length files, putting pressure on the system with slab only allocations. On exit the script prints out how many bytes were read by the read-file program. The results are as follows Without patch: /mnt/btrfs-test/reads/file1: total read during loops 27262988288 /mnt/btrfs-test/reads/file2: total read during loops 27262976000 With patch: /mnt/btrfs-test/reads/file2: total read during loops 18640457728 /mnt/btrfs-test/reads/file1: total read during loops 9565376512 This patch results in a 50% reduction of the amount of pages evicted from our working set. Signed-off-by: Josef Bacik <jbacik@fb.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> |
||
---|---|---|
arch | ||
block | ||
certs | ||
crypto | ||
Documentation | ||
drivers | ||
firmware | ||
fs | ||
include | ||
init | ||
ipc | ||
kernel | ||
lib | ||
mm | ||
net | ||
samples | ||
scripts | ||
security | ||
sound | ||
tools | ||
usr | ||
virt | ||
.cocciconfig | ||
.get_maintainer.ignore | ||
.gitattributes | ||
.gitignore | ||
.mailmap | ||
COPYING | ||
CREDITS | ||
Kbuild | ||
Kconfig | ||
MAINTAINERS | ||
Makefile | ||
README |
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.