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[Dan Streetman <dan.streetman@xxxxxxxxxxxxx>]

** Description changed:

  [Impact]
  
  A user reports that cachefilesd will spin at 100% of a cpu when started
  on a filesystem where the free space is less than the bcull threshold
  and culling the cache is insufficient to free up space.
  
  Investigation shows that this is because cachefilesd detects that
  culling is required, tries to cull, and does not realise that culling
  cannot free up enough space, so just keeps retrying.
  
- [Testing/Reproducing]
+ [Test Case]
  
  I created a VM with a spare disk, mounted it to /raid (or whatever).
  I changed the /etc/default/cachefilesd to start at boot, filled the /raid filesystem to over the bcull threshold, and started cachefilesd. When running top, the cachefilesd process is at the top using approx 100% of 1 CPU. It appears to be trying to free up space in the cache (that is not even used) because the filesystem is over the threshold for culling.
+ 
+ [Regression Potential]
+ 
+ The patch makes changes to how cachefilesd detects if it should sleep
+ or cull, so regressions would be in the area of cachefilesd spinning
+ instead of sleeping (which is what it does now) or sleeping instead
+ of culling.
+ 
+ However the patch is small and easily understood and backports with
+ minimal effort.
  
  [Fix]
  
  This is fixed upstream in 0.10.6:
  
  * Wed Feb 3 2016 David Howells <dhowells@xxxxxxxxxx> 0.10.6-1
  ...
  - Suspend culling when cache space is short and cache objects are pinned.
  
  The particular patch is ce353f5b6b5b ("cachefilesd can spin when disk
  space is short.")
- 
- [Regression Potential]
- The patch is small and easily understood and backports with minimal effort.

** Description changed:

  [Impact]
  
  A user reports that cachefilesd will spin at 100% of a cpu when started
  on a filesystem where the free space is less than the bcull threshold
  and culling the cache is insufficient to free up space.
  
  Investigation shows that this is because cachefilesd detects that
  culling is required, tries to cull, and does not realise that culling
  cannot free up enough space, so just keeps retrying.
  
  [Test Case]
  
  I created a VM with a spare disk, mounted it to /raid (or whatever).
  I changed the /etc/default/cachefilesd to start at boot, filled the /raid filesystem to over the bcull threshold, and started cachefilesd. When running top, the cachefilesd process is at the top using approx 100% of 1 CPU. It appears to be trying to free up space in the cache (that is not even used) because the filesystem is over the threshold for culling.
  
  [Regression Potential]
  
  The patch makes changes to how cachefilesd detects if it should sleep
  or cull, so regressions would be in the area of cachefilesd spinning
  instead of sleeping (which is what it does now) or sleeping instead
  of culling.
  
  However the patch is small and easily understood and backports with
  minimal effort.
  
- [Fix]
+ [Other Info]
  
  This is fixed upstream in 0.10.6:
  
  * Wed Feb 3 2016 David Howells <dhowells@xxxxxxxxxx> 0.10.6-1
  ...
  - Suspend culling when cache space is short and cache objects are pinned.
  
  The particular patch is ce353f5b6b5b ("cachefilesd can spin when disk
  space is short.")

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https://bugs.launchpad.net/bugs/1810372

Title:
  Infinite busy-loop trying to cull when cache space is short

Status in cachefilesd package in Ubuntu:
  Confirmed
Status in cachefilesd source package in Xenial:
  New

Bug description:
  [Impact]

  A user reports that cachefilesd will spin at 100% of a cpu when
  started on a filesystem where the free space is less than the bcull
  threshold and culling the cache is insufficient to free up space.

  Investigation shows that this is because cachefilesd detects that
  culling is required, tries to cull, and does not realise that culling
  cannot free up enough space, so just keeps retrying.

  [Test Case]

  I created a VM with a spare disk, mounted it to /raid (or whatever).
  I changed the /etc/default/cachefilesd to start at boot, filled the /raid filesystem to over the bcull threshold, and started cachefilesd. When running top, the cachefilesd process is at the top using approx 100% of 1 CPU. It appears to be trying to free up space in the cache (that is not even used) because the filesystem is over the threshold for culling.

  [Regression Potential]

  The patch makes changes to how cachefilesd detects if it should sleep
  or cull, so regressions would be in the area of cachefilesd spinning
  instead of sleeping (which is what it does now) or sleeping instead
  of culling.

  However the patch is small and easily understood and backports with
  minimal effort.

  [Other Info]

  This is fixed upstream in 0.10.6:

  * Wed Feb 3 2016 David Howells <dhowells@xxxxxxxxxx> 0.10.6-1
  ...
  - Suspend culling when cache space is short and cache objects are pinned.

  The particular patch is ce353f5b6b5b ("cachefilesd can spin when disk
  space is short.")

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