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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Is the iSCSI block device having client side-read cache (if yes how to disable)?

I have a remote block device with the test ext4 filesystem image. On the iSCSI initiator side, I have this device detected as let's say /dev/sdb. I am not mounting this filesystem but instead I use ...
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1answer
25 views

Using terminal to reset icon cache - which method?

I've been trying to find out how to reset the icon cache on my MacBook, and two methods seem to always be suggested. However, the two approaches differ slightly in the third line. Method 1 sudo find ...
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30 views

SSD + HDD performance from power on

I'm planing to buy a new laptop with a 128GB SSD and a 1TB HDD. And I would like to have reliability, performance and storage space from power up and during the whole runing time. During the running ...
3
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0answers
47 views

LVM cache and TRIM

I have set up LVM to cache a logical volume (located on an HDD) on a partition of an SSD (in writeback mode if this matters). As far as I can tell, this works correctly and the cache uses all ...
3
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0answers
50 views

How to cache block devices (for device mapper)?

problem / observed effect It seems that the page cache ignores block devices which are not opened. And worse: Reads from device mapper (DM) devices which use a cached device are not cached at all ...
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30 views

One SSD cache for two partitions on two separate disks?

I have two hard drives: one for my operating system and the other for other data. I recently bought an SSD drive that I would like to use an LVM cache for those two devices. The problem is that I ...
4
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116 views

Why are slab objects not reclaimed automatically

Everyday after a full system backup, various programs are failing with read errors until I run echo 2 > /proc/sys/vm/drop_caches to free reclaimable slab objects. For example, here's the output of ...
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2answers
56 views

how does o_sync trigger pdflush?

When I write using o_sync, the write call returns once the data has been written to the disk. But how does o_sync force Linux to write the data to disk? Normally you would have to wait a maximum of ...
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61 views

OpenLDAP as a Proxy cache only, no local database

I am trying to get a local LDAP proxy cache running. The idea is this: Currently a computer (A) is sending all ldap requests to a remote ldap server (L) Instead of that, there should be a proxy ...
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0answers
24 views

SSD as write target during reads

I have a real-time application which always writes data to a RAID 10 HDD configuration in a sequential manner at around ~50 MB/s. It uses mmap and writing should never be blocked due to waiting I/O. ...
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1answer
73 views

how to increase cache memory in centos

I have been facing a insuffient space in "/var/cache/yum" directory. due to this my gui of centos crashes.i want to increase the size of cache directory. also want to know the actual size of cache ...
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22 views

Which subsystem caches file reads?

I am trying to understand how exactly file reads are served from Page Cache. This will be useful when I will be implementing my own filesystem in the kernel. Is file content cached by VFS or ...
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1answer
75 views

Linux top -n 1 Command doesn't get update

I'm calling the Linux top -n 1 -b command from a Qt application to get the free CPU percentage. This application calls this command every 3 seconds, but the CPU usage seems to be updated only the ...
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1answer
27 views

Reset Bash's memory used for auto-complete

After renaming a file to a similar name, I noticed TAB was still completing the old filename (if it matched the letters so far) and not showing the new one. No matter how many letters I typed, it ...
2
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1answer
26 views

Is partition created by dd (and cached) instantly available for writing

I'm creating a partition (from backup) with dd and need to know if there is a need of some sort of sync/timeout before I can access it. As I know data may be cached in dirty pages. But what if I ...
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37 views

How to configure some proxy like Squid to download specific URL only once?

I have read article about Windows 10 spying my activity and blocked all mentioned addresses on my router's firewall. This included addresses az361816.vo.msecnd.net and az512334.vo.msecnd.net ...
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0answers
26 views

what is left inside the cache even after clearing the page cache data?

I was trying to clear the cache using echo 3 > /proc/sys/vm/drop_caches Even after performing the above operation there remain some space inside the cache? When I check with free -m around it ...
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1answer
140 views

Using readahead in Debian Jessie

The article BootProcessSpeedup on the Debian Wiki lists a tip to speed up boot time. It says to install readahead and then #touch /etc/readahead/profile-once. It seems like an outdated article, ...
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1answer
45 views

Linux Gateway as Download Accelerator like IPCop's

We're running dnsmasq on a linux box inside our network for DHCP and DNS. I would like to add a download accelerator like IPCop's (http://blockouttraffic.de/ua_index.php) but without having IPCop as ...
4
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1answer
222 views

How does Linux handle block devices?

Today I learned that FreeBSD removed support for block devices entirely. While reading their rational for the decision I came across this: Block devices are disk devices for which the kernel ...
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2answers
133 views

Force dig to forget records

I would like to let dig always forget a DNS record. I mean if I do dig yahoo.com then I have a record back in with ttl for 1790 seconds. Even if I have no cache service installed, next time i do the ...
5
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1answer
97 views

How to enable package caching in dnf?

I started using fedora 22 and started learning dnf only to find out about two annoying facts: Almost every time I install or upgrade anything it has to rebuild the whole repository metadata cache ...
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1answer
62 views

why does my Ubuntu Virtual Machine slow down after a number of searches, and builds?

I recently learned that my Ubuntu Linux file system may cache the result of some commands such as searches, sorts, and perhaps build commands such as make. I run Ubuntu in a VM, and although I have ...
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17 views

CVMFS file access slow, although file is in cache

I have a directory in which there is a symlink to a file on CVMFS. When I first boot up, and do ls, it takes a long time (~a minute). The reason is that ls does fstat on each file to determine what ...
3
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1answer
122 views

How to run free command by crontab

I want to run this command: free && sync && echo 3 > /proc/sys/vm/drop_caches && free -m by cron. That way I can free my RAM and cache in an Ubuntu system. I'm using ...
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106 views

Opcache and shared memory issue

I installed zend_opcache on my server box , but I can not increase opcache.memory_consumption over 1600 . (example : 2048) . after increase following error occur in server : Fatal Error Fatal Error ...
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61 views

Will btrfs snapshots ever share page cache?

It's common to run multiple container images based on the same parent. In theory you should be able to share page cache between these containers automatically. E.g. some of the code in shared ...
2
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1answer
40 views

Directory traversal cache eviction despite having plenty of memory?

I have a huge Mercurial repository (take a guess how many directories it has -- it's gonna be more than you guessed). The time taken to do basic repository operations is heavily dependent on whether ...
3
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0answers
40 views

What could cause dropping cache to be extremely slow on a large cluster?

I'm attempting to time file I/O on my disks. In order to make sure all the I/O is happening off the hard drives and not from ram, before I time any read, I run a drop cache command. Specifically, I ...
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1answer
145 views

What is ~/.cache/weather.xml?

I use a clock-date-weather conky and I noticed that it is related to the file ~/.cache/weather.xml. I am curious: was this file created by conky or by what other program? Is it present on the system ...
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0answers
330 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 ...
15
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3answers
1k 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
52 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
127 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 ...
5
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0answers
148 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
61 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
80 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 ...
1
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1answer
47 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
123 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
121 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
109 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 # ...
4
votes
2answers
264 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 ...
1
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0answers
107 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
418 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 ...
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0answers
75 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 ...
4
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2answers
140 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
votes
1answer
83 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 ...
3
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0answers
112 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 ...
1
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1answer
216 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
150 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 ...