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When reading a btree node, at read_block_for_search(), if we don't find the node's (or leaf) extent buffer in the cache, we will read it from disk. Since that requires waiting on IO, we release all upper level nodes from our path before reading the target node/leaf, and then return -EAGAIN to the caller, which will make the caller restart the while btree search. However we are causing the restart of btree search even for cases where it is not necessary: 1) We have a path with ->skip_locking set to true, typically when doing a search on a commit root, so we are never holding locks on any node; 2) We are doing a read search (the "ins_len" argument passed to btrfs_search_slot() is 0), or we are doing a search to modify an existing key (the "cow" argument passed to btrfs_search_slot() has a value of 1 and "ins_len" is 0), in which case we never hold locks for upper level nodes; 3) We are doing a search to insert or delete a key, in which case we may or may not have upper level nodes locked. That depends on the current minimum write lock levels at btrfs_search_slot(), if we had to split or merge parent nodes, if we had to COW upper level nodes and if we ever visited slot 0 of an upper level node. It's still common to not have upper level nodes locked, but our current node must be at least at level 1, for insertions, or at least at level 2 for deletions. In these cases when we have locks on upper level nodes, they are always write locks. These cases where we are not holding locks on upper level nodes far outweigh the cases where we are holding locks, so it's completely wasteful to retry the whole search when we have no upper nodes locked. So change the logic to not return -EAGAIN, and make the caller retry the search, when we don't have the parent node locked - when it's not locked it means no other upper level nodes are locked as well. Reviewed-by: Josef Bacik <josef@toxicpanda.com> Signed-off-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: David Sterba <dsterba@suse.com> |
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| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
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.