[Gluster-users] Questions about gluster/fuse, page cache, and coherence

nlxswig nlxswig at 126.com
Mon Mar 18 07:03:20 UTC 2013

Good questions, 
Why are there no reply?

At 2011-08-16 04:53:50,"Patrick J. LoPresti" <lopresti at gmail.com> wrote:
>(FUSE developers:  Although my questions are specifically about
>Gluster, I suspect most of the answers have more to do with FUSE, so I
>figure this is on-topic for your list.  If I figured wrong, I
>I have done quite a bit of searching looking for answers to these
>questions, and I just cannot find them...
>I think I understand how the Linux page cache works for an ordinary
>local (non-FUSE) partition.  Specifically:
>1) When my application calls read(), it reads from the page cache.  If
>the page(s) are not resident, the kernel puts my application to sleep
>and gets busy reading them from disk.
>2) When my application calls write(), it writes to the page cache.
>The kernel will -- eventually, when it feels like it -- flush those
>dirty pages to disk.
>3) When my application calls mmap(), page cache pages are mapped into
>my process's address space, allowing me to create a dirty page or read
>a page by accessing memory.
>4) When the kernel reads a page, it might decide to read some other
>pages, depending on the underlying block device's read-ahead
>parameters.  I can control these via "blockdev".  On the write side, I
>can exercise some control with various VM parameters (dirty_ratio
>etc).  I can also use calls like fsync() and posix_fadvise() to exert
>some control over page cache management at the application level.
>My question is pretty simple.  If you had to re-write the above four
>points for a Gluster file system, what would they look like?  If it
>matters, I am specifically interested in Gluster 3.2.2 on Suse Linux
>Enterprise Server 11 SP1 (Linux + whatever Suse does to
>their kernels).
>Does Gluster use the page cache on read()?  On write()?  If so, how
>does it ensure coherency between clients?  If not, how does mmap()
>work (or does it not work)?
>What read-ahead will the kernel use?  Does posix_fadvise(...,
>POSIX_FADV_WILLNEED) have any effect on a Gluster file system?
>I find it hard to imagine that I am the only person with questions
>like these...  Did I miss a FAQ list somewhere?
> - Pat
>Gluster-users mailing list
>Gluster-users at gluster.org
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