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Re: [Cluster-devel] [RFC] readdirplus implementations: xgetdents vs dirreadahead syscalls


On 25/07/14 18:52, Zach Brown wrote:
On Fri, Jul 25, 2014 at 01:37:19PM -0400, Abhijith Das wrote:
Hi all,

The topic of a readdirplus-like syscall had come up for discussion at last year's
LSF/MM collab summit. I wrote a couple of syscalls with their GFS2 implementations
to get at a directory's entries as well as stat() info on the individual inodes.
I'm presenting these patches and some early test results on a single-node GFS2

1. dirreadahead() - This patchset is very simple compared to the xgetdents() system
call below and scales very well for large directories in GFS2. dirreadahead() is
designed to be called prior to getdents+stat operations.
Hmm.  Have you tried plumbing these read-ahead calls in under the normal
getdents() syscalls?

We don't have a filereadahead() syscall and yet we somehow manage to
implement buffered file data read-ahead :).

- z

Well I'm not sure thats entirely true... we have readahead() and we also have fadvise(FADV_WILLNEED) for that. It could be added to getdents() no doubt, but how would we tell getdents64() when we were going to read the inodes, rather than just the file names? We may only want to readahead some subset of the directory entries rather than all of them, so the thought was to allow that flexibility by making it, its own syscall,


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