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We sometimes have to allocate new extent states when clearing or setting new bits in an extent io tree. Generally we preallocate this before taking the tree spin lock, but we can use this preallocated extent state sometimes and then need to try to do a GFP_ATOMIC allocation under the lock. Unfortunately sometimes this fails, and then we hit the BUG_ON() and bring the box down. This happens roughly 20 times a week in our fleet. However the vast majority of callers use GFP_NOFS, which means that if this GFP_ATOMIC allocation fails, we could simply drop the spin lock, go back and allocate a new extent state with our given gfp mask, and begin again from where we left off. For the remaining callers that do not use GFP_NOFS, they are generally using GFP_NOWAIT, which still allows for some reclaim. So allow these allocations to attempt to happen outside of the spin lock so we don't need to rely on GFP_ATOMIC allocations. This in essence creates an infinite loop for anything that isn't GFP_NOFS. To address this we may want to migrate to using mempools for extent states so that we will always have emergency reserves in order to make our allocations. Signed-off-by: Josef Bacik <josef@toxicpanda.com> Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: David Sterba <dsterba@suse.com> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
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.