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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.

3
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proceeds to just hang, possibly for minutes. The article predicted a simple change to the kernel defaults. On 64-bit x86, the writeback cache was allowed to grow to 20% of system RAM by default …
asked Oct 9 '18 by sourcejedi
2
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RAM to build up large amounts writes in the page cache, which can take a long time to write out. The kernel already had some code designed to avoid "USB-stick stalls". This is the "No-I/O dirty … throttling" code. This code was also described on LWN, in 2011. It throttles write() calls to control both the size of the overall writeback cache, and the proportion of writeback cache used for the …
answered Oct 9 '18 by sourcejedi
8
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(applied in kernel v3.14). In the question, we said the default limit was set to 20% of memory. Actually, it is set to 20% of memory which is available for dirty page cache. For example the kernel … buffers sent data for TCP/IP network sockets. The socket buffers cannot be dropped and replaced with dirty page cache :-). The problem was that the kernel was counting swappable memory, as if it …
answered Nov 7 '18 by sourcejedi
0
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0answers
freeze at all. 2) I went on to read more than the size of my RAM, and that did not freeze either: $ free -h total used free shared buff/cache available Mem … cache, so that subsequent reads of the same data can be fulfilled much more quickly. E.g. 5.3 GB/s instead of 188 MB/s :-). These examples are reading from a block device. In the case of a block device …
asked May 14 by sourcejedi
2
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The page cache is stored in RAM. In principle, it can fill the entire physical memory. The reason that it does not, is that memory is also used for other purposes. "Anonymous" (swap-backed) memory … allocations compete with the file-backed allocations of the page cache. The two are balanced by the memory management code. The exact behaviour of the memory management is ferociously complicated …
answered Jul 20 by sourcejedi
5
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Sounds like you do have a problem Yeah, so if the cache includes the tracker database, when you "clean" it you're just going to get it rebuilt again (after laboriously scanning all of your files … do this to ~/.cache, so you're likely to hit some untested corner cases that blow up. E.g. I notice that ls -l --time=atime ~/.cache/tracker shows a fair amount of variation, so I'm afraid that's …
answered May 8 '16 by sourcejedi
7
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1answer
with a 64-bit kernel, the dirty page cache (aka writeback cache) was allowed to grow to 20% of memory by default. With a 32-bit kernel, it was effectively limited to ~180MB. Linus suggested limiting … ). It shows the kernel should have been controlling the dirty page cache on a per-device basis: No-I/O dirty throttling - LWN.net, 2011 That is where Fengguang's patch set comes in. He is …
asked Nov 7 '18 by sourcejedi
1
vote
Shmem: 19327344 kB You have 19GB in tmpfs, or some other shared memory object. It's often tmpfs. Check df -h -t tmpfs. System V shared memory can be shown by ipcs -m. Some, but not all, o …
answered Nov 23 '18 by sourcejedi
2
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When the program closes the block device file, Linux flushes the associated cache, forcing the program to wait. This only applies to the last close() however. It will not happen if something else … (dmesg). As well as waiting for all the cached writes, the last close() also drops all of the cache (kill_bdev()). I have verified this for myself, by watching the output of the free command. linux-4.20 …
answered Feb 18 by sourcejedi
1
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0answers
[PATCH 0/8] Throttled background buffered writeback v7 Since the dawn of time, our background buffered writeback has sucked. When we do background buffered writeback, it should have little i …
asked Nov 21 '18 by sourcejedi
11
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2answers
$ free -h total used free shared buff/cache available Mem: 501M 146M 19M 9.7M 335M 331M Swap: 1.0G … 85M 938M $ free -w -h total used free shared buffers cache available Mem: 501M 146M 19M 9.7M 155M 180M …
asked Apr 28 '18 by sourcejedi
10
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What is the difference between "buffer", and the other cache? Why do we see this distinction so prominently? (Possible historical reason) What are Buffers used for? Why might we expect Buffers in … particular to be larger or smaller? 1. What is the difference between "buffer", and the other type of cache? Buffers reports the amount of page cache used for block devices. The kernel has to …
answered Apr 28 '18 by sourcejedi
2
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"buff/cache". It includes all your tmpfs files. It also includes "shared" memory which is allocated from a secret kernel tmpfs :-). This includes "system V shared memory", and also some types of … graphics buffers. Anyway, those two mistakes roughly cancel out. So what about the rest of the memory? When you drop caches in Linux, it chooses not to drop any cache which is mapped by a currently …
answered Nov 10 '16 by sourcejedi
0
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2answers
Dirty %lu - Memory which is waiting to get written back to the disk. Writeback %lu - Memory which is actively being written back to the disk. -- man proc Does Dirty include Writeback? …
asked Nov 14 '18 by sourcejedi
0
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These settings only take effect after the total write-back cache has filled up to (dirty_ratio + dirty_background_ratio / 2). References: LKML post by Jan Kara commit 5fce25a9df48 in v2.6.24. "We …
answered Nov 16 '18 by sourcejedi

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