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For defrag, we don't really want to use btrfs_get_extent() to iterate
all extent maps of an inode.
The reasons are:
- btrfs_get_extent() can merge extent maps
And the result em has the higher generation of the two, causing defrag
to mark unnecessary part of such merged large extent map.
This in fact can result extra IO for autodefrag in v5.16+ kernels.
However this patch is not going to completely solve the problem, as
one can still using read() to trigger extent map reading, and got
them merged.
The completely solution for the extent map merging generation problem
will come as an standalone fix.
- btrfs_get_extent() caches the extent map result
Normally it's fine, but for defrag the target range may not get
another read/write for a long long time.
Such cache would only increase the memory usage.
- btrfs_get_extent() doesn't skip older extent map
Unlike the old find_new_extent() which uses btrfs_search_forward() to
skip the older subtree, thus it will pick up unnecessary extent maps.
This patch will fix the regression by introducing defrag_get_extent() to
replace the btrfs_get_extent() call.
This helper will:
- Not cache the file extent we found
It will search the file extent and manually convert it to em.
- Use btrfs_search_forward() to skip entire ranges which is modified in
the past
This should reduce the IO for autodefrag.
Reported-by: Filipe Manana <fdmanana@suse.com>
Fixes:
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|---|---|---|
| arch | ||
| 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.