cache is a component that stores data so future requests for that data can be served faster; the data stored in a cache might be the results of an earlier computation, or the duplicates of data stored elsewhere.

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39 views

ssd caching in loop device on btrfs

I have an ssd and 2TB hard disk. The ssd is used for the root filesystem which uses only around 20G of the 120G available. Is there a way to use an image/loop on the root filesystem (btrfs) as a cache ...
13
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3answers
790 views

Is it safe to remove ~/.cache?

When I scanned my $HOME directory with baobab (Disk Usage Analyzer), I found that ~/.cache is consuming about half a GB. I also tried to restart and again check size but no difference. So, I am ...
3
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0answers
9 views

Is posix_fadvice / POSIX_FADV_DONTNEED functional in Linux?

If I am doing once only scanning across big files then do I need to worry about impact on the page cache or does the OS take care to avoid my scan causing pointless churn in the page cache. I want to ...
3
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1answer
50 views

Linux doesn't drop FS Caches. Instead Memory starts Swapping

I'm quite confused about this behaviour of linux memory caching. total used free shared buffers cached Mem: 15953 14188 1765 64 ...
3
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0answers
46 views

Limit the inode cache used by a command

I want to run a task with limits on the kernel objects that they will indirectly trigger. Note that this is not about the memory, threads, etc. used by the application, but about memory used by the ...
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2answers
39 views

Precaching the list of files of the filesystem

I was wondering where and in what form a list of files and directories is stored on the ext4 filesystem. The problem is that whenever I try to access a certain directory for the first time since boot ...
5
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1answer
39 views

What memory is not used by processes and freed by `echo 3 > /proc/sys/vm/drop_caches`?

Without programs open, my computer uses about 512M of memory. Yesterday, I had nothing open, yet 2 GB of mem use (used - cache = 2153): total used free shared buffers ...
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1answer
29 views

Reading ELF file after dropping caches

I have an eMMC backed Linux 3.10 development device (Android) and I am trying to better understand when Linux is actually reading from the eMMC as opposed to the page cache. Specifically, I am ...
1
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1answer
34 views

Change Linux Bcache device type

I have accidentally configured my SSD as a backing device instead of a caching device. Simply trying either one of the following: sudo make-bcache -C /dev/sdb1 sudo make-bcache -C /dev/sdb Gives ...
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0answers
53 views

how to clear NFS client side cache and server side cache?

I would like to know what is the cache size NFS is using at client side and server side. How to clear it.? Is there a difference between system cache and network cache ?
3
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0answers
55 views

How to generate graphs from lmbench results?

I need to use the lmbench benchmarking tool to get the system performance statistics. I am able to execute and run the results. In the results folder this is a MakeFile with this information # ...
3
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2answers
54 views

How and where is file system meta data cached in Linux

My earlier question apparently had a wrong premise. I thought file system meta data was cached in the inode and dentry cache, but apparently not. When I do: # time find . > /dev/null real ...
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0answers
49 views

Out of Memory with unused memory and swap

I have a strange error on my Raspberry Pi2. System is archlinuxarm. Short after boot (about 30 secs), the system states that it is out of memory, resulting in closing many applications, most time ...
2
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1answer
67 views

how to check default cache mode for disk in kvm

KVM/qemu support various types of cache - none, writethrough, writeback. How to check which one is default and is used on system when no cache= is specified? For RHEL6 i found that it's writethrough ...
0
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0answers
39 views

Linux - is it possible to limit VFS cache usage on a per-process basis

I'm trying to investigate performance degradations while running background copy operations (using dd to write or read large disk-images). Is it possible to limit VFS cache usage for a single ...
3
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2answers
57 views

How to determine whether the data is written to disk or cached?

I'm learning file operation calls under Linux. The read() and write() and many other functions use cache to increase performance, and I know fsync() can transfer data from cache to disk device. ...
2
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1answer
47 views

How to get all CPU cache information without SU access

I am trying to find out the cache mapping scheme for all the levels of class of a linux server, however I do not have root access. I would just use DMIdecode for this but you need root access. Is ...
0
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0answers
86 views

Using Varnish + Nginx Forcing SSL

i'm using Varnish and i would like to force communication only with SSL. My server is Nginx. What's the best way to do so? Or the easiest? I read about Pound proxy and installed it but guides were too ...
3
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0answers
70 views

Discover what is cached by dm-cache

I am using dm-cache successfully for quite a while now. Now I would like to know which files are being currently in the cache. I understand that dm-cache works with blocks, not files, but since there ...
0
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0answers
93 views

Booting from an lvm-cached volume

I created a cache pool following this article. The process seems to be successful. After doing an upgrade-grub and rebooting, Grub complains that it can not find the root volume (showing a UUID). - ...
2
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0answers
74 views

Restore /var/cache files

I've accidentally deleted all contents of /var/cache files. I managed to reinstall most by doing dpkg -S /var/cache and apt-get --reinstall install PACKAGE_NAME (see here) on every package that I've ...
3
votes
1answer
64 views

Cache directory and file list to prevent hard drive access when browsing contents

I have 7 hard drives that are in a virtual pool (mhddfs) so they appear as one directory. I put them to sleep after 5 minutes of inactivity to save a significant chunk of power. The problem with this ...
0
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1answer
177 views

How to enable a non-root user to empty the linux buffer cache

I'm required to empty the linux buffer cache in a python script, that runs on a Debian wheezy VM. As root I run sync; echo 3 | sudo tee /proc/sys/vm/drop_caches, but the script is run by a user, ...
5
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1answer
285 views

List all files that are present in the cache

This question answers to the question on how to find the what is part of cache. However, in the fincore executable you have to pass the filename to check if it is part of cache. Is there a tools or a ...
2
votes
3answers
85 views

Buffering (named) pipe in GNU OS

In the GNU OS a process can only write data to a pipe if another process reads the same data (from the same pipe) at the same time. Is there something like a pipe which lets the 1st process write and ...
1
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0answers
45 views

How shareable is /var/cache?

I know that some subdirectories of /var/cache are pretty much shareable, for example /var/cache/pacman (in case of ArchLinux), and possibly others (/var/cache/man?), but at least /var/cache/ldconfig ...
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2answers
64 views

Increasing performance of clear text file reads

In our bioinformatics application we have large files (up to 900MB, typically 100MB). These files contain a clear text representation of a genome, and are essentially a 1 line file with a sequence of ...
1
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1answer
190 views

Request header for Cache-Control not working

I have set Cache-Control in apache for 1 week for my JS Files but when i check in the browser Cache-Control shows no-cache. Where i am missing the configuration ? Below is my configuration in apache ...
4
votes
1answer
72 views

Avoid -dbg_version packages on apt-cacher-ng server

Intro: We have created a apt-cacher-ng server to provide cached packages to our users that have Ubuntu 14.04 installed. Combined with the cached packages, we are doing a weekly "mirror" of some Ubuntu ...
0
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2answers
94 views

Memcached on a webserver

We host a Magento webshop hosted by Amazon EC2, and we have speed issues. We're currently looking at moving to another provider. We found one hosting provider where we have a test account now. Speed ...
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0answers
35 views

Very strange issue, something is blocking specific links on local domain

I have a very strange issue and I ran out of ideas. The major problem is that the symptoms are not consistent. I have a short link website hosted on 2 virtual machines, one with nginx+php-fpm and one ...
1
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1answer
194 views

file access time after loading file into the cache

I read from here that I could load file into RAM for faster accessing using the below command. cat filename > /dev/null However, I wanted to test if the above statement is really true. So, I ...
0
votes
1answer
221 views

Difference between route cache and neighbor table

Our Ubuntu server runs as a router for thousands of devices. With the growing number of connecting clients we have noticed 3 overflow problems in the kernel log: 1. Route cache chain too long 2. ...
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0answers
315 views

Ubuntu: Restore not printed document from browser cache

I was at work today faced with a situation where I have to prove that I did not make a mistake. Without going into detail, yesterday I generated an important document which was to be printed. For ...
2
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1answer
106 views

What is being cached?

I have an embedded system with a low amount of memory. The system has allocation issues. Maybe due to fragmentation: Memory allocation issue on NOMMU? The platform is a NOMMU platform and so I suspect ...
0
votes
1answer
52 views

What dev folder allows you tell the OS to cache something?

Someone told me that there is a sub folder off of dev that basically allows you to tell the OS to keep the contents of that folder cached in RAM. So if I put some files & directories in ...
3
votes
1answer
384 views

Fix “Route hash chain too long” without restart

On our production server (ubuntu 12.04, 3.2.0-63 kernel) routing cache reached its capacity. Modifying rhash_entries is out of the question, since it is a kernel boot param, and we can not restart the ...
5
votes
2answers
295 views

How should I restore /var/cache?

I just restored my Raspberry Pi server from an rsync image. During the backup, I had excluded /var/cache/*, thinking that this would restore an empty directory. This worked, but when I rebooted, a ...
3
votes
1answer
267 views

Spawn multiple dirty page flusher threads per device

In earlier 2.6.X kernels, pdflush was used and it would spawn more pdflush threads if all current pdflush threads were busy for a second (read from The Linux Page Cache and pdflush). Since the ...
3
votes
1answer
107 views

Artificially prime buffer cache?

Is it beneficial to artificially prime the buffer cache when dealing with larger files? Here's a scenario: A large file needs to be processed, line by line. Conceptually, it is easy to parallelize ...
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0answers
32 views

Can not analyze output from Squid and varnish

I'm using one Squid server between tow cache server. I get from headers following information: X-Cache MISS, HIT from cache-zz X-Cache-Age 515 X-Cache-Control public, max-age=3600 X-Cache-Lookup HIT ...
0
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0answers
18 views

how to find where buffers/cache are and how to clean them up? [duplicate]

I want to create 20gb ram disk for ANSYS to work in yet on free -g I see: And personally I have not created any ram drives yet. So I wonder how to maximize avaliable ram: how to locate what is using ...
2
votes
0answers
133 views

Reduce cache size of flash storage devices

For various benefits Linux uses a memory cache for writes to removable stogare devices like memory sticks. This cache seems to be quite large on my system, which leads to some annoying behavior. For ...
2
votes
0answers
49 views

In meminfo, sometimes Mapped more than Cached

In /proc/meminfo, AFAIK Cached >= Mapped But after /proc/sys/vm/drop_caches, it goes to Cached < Mapped Cached: 66132 kB Mapped: 67792 kB /proc/meminfo contents ...
3
votes
1answer
8k views

Is no caching mode page a serious error?

My server log displays the following error messages in RED: kernel: sda: sda1 sda2 kernel: sd 0:1:0:0: [sda] No Caching mode page found kernel: sd 0:1:0:0: [sda] Assuming drive cache: write through ...
3
votes
0answers
96 views

Figuring out physical cache layout in FreeBSD

I'm trying to figure out they physical cache layout of my CPU in FreeBSD 10. I see the following from sysctl kern.sched.topology_spec kern.sched.topology_spec: <groups> <group level="1" ...
1
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2answers
148 views

Random application crashes in Linux

Sometimes after booting my computer, some applications fail to start: they crash. They're usually the largest ones, such as firefox, thunderbird or virtualbox. Rebooting or cleaning the cache usually ...
0
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1answer
236 views

should I reduce /dev/shm size?

I have a server wity 8 GB RAM Mem: Total 8031464 Used 5146344 Free 2885120 If I execute # df it always returns this tmpfs 4015732 0 4015732 0% /dev/shm What does it ...
1
vote
1answer
864 views

Clear Memory Cache on Amazon EC2

In our project we have a few tests which run for about 3-4 hours continuously. In due course, the tests fail as they couldn't find enough memory. On googling, I found that running the following ...
6
votes
1answer
615 views

How to use an SSD for caching, so my hard disks can spin down?

I've got a file server with a bunch of disks running together in a BTRFS pool and want to add an SSD for caching. I'm not mainly after speeding up things, but want to catch the regular small accesses ...