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19b9ad6731
The comment claims that this helper will try not to loose bits, but for 64bit long it looses the high bits before hashing 64bit long into 32bit int. Use the helper hash_long() to do the right thing for 64bit long. For 32bit long, there is no change. All the callers of end_name_hash() either assign the result to qstr->hash, which is u32 or return the result as an int value (e.g. full_name_hash()). Change the helper return type to int to conform to its users. [ It took me a while to apply this, because my initial reaction to it was - incorrectly - that it could make for slower code. After having looked more at it, I take back all my complaints about the patch, Amir was right and I was mis-reading things or just being stupid. I also don't worry too much about the possible performance impact of this on 64-bit, since most architectures that actually care about performance end up not using this very much (the dcache code is the most performance-critical, but the word-at-a-time case uses its own hashing anyway). So this ends up being mostly used for filesystems that do their own degraded hashing (usually because they want a case-insensitive comparison function). A _tiny_ worry remains, in that not everybody uses DCACHE_WORD_ACCESS, and then this potentially makes things more expensive on 64-bit architectures with slow or lacking multipliers even for the normal case. That said, realistically the only such architecture I can think of is PA-RISC. Nobody really cares about performance on that, it's more of a "look ma, I've got warts^W an odd machine" platform. So the patch is fine, and all my initial worries were just misplaced from not looking at this properly. - Linus ] Signed-off-by: Amir Goldstein <amir73il@gmail.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> |
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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.
See Documentation/00-INDEX for a list of what is contained in each file.
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.