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c8eaeac7b7
With the per-inode block reserves we started refilling the reserve based on the calculated size of the outstanding csum bytes and extents for the inode, including the amount we were adding with the new operation. However, generic/224 exposed a problem with this approach. With 1000 files all writing at the same time we ended up with a bunch of bytes being reserved but unusable. When you write to a file we reserve space for the csum leaves for those bytes, the number of extent items required to cover those bytes, and a single transaction item for updating the inode at ordered extent finish for that range of bytes. This is held until the ordered extent finishes and we release all of the reserved space. If a second write comes in at this point we would add a single reservation for the new outstanding extent and however many reservations for the csum leaves. At this point we find the delta of how much we have reserved and how much outstanding size this is and attempt to reserve this delta. If the first write finishes it will not release any space, because the space it had reserved for the initial write is still needed for the second write. However some space would have been used, as we have added csums, extent items, and dirtied the inode. Our reserved space would be > 0 but less than the total needed reserved space. This is just for a single inode, now consider generic/224. This has 1000 inodes writing in parallel to a very small file system, 1GiB. In my testing this usually means we get about a 120MiB metadata area to work with, more than enough to allow the writes to continue, but not enough if all of the inodes are stuck trying to reserve the slack space while continuing to hold their leftovers from their initial writes. Fix this by pre-reserved _only_ for the space we are currently trying to add. Then once that is successful modify our inodes csum count and outstanding extents, and then add the newly reserved space to the inodes block_rsv. This allows us to actually pass generic/224 without running out of metadata space. Signed-off-by: Josef Bacik <josef@toxicpanda.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.