Another parallel effort could be trying to configure the number of inodes/dentries cached by kernel VFS using /proc/sys/vm interface.
============================================================== vfs_cache_pressure ------------------ This percentage value controls the tendency of the kernel to reclaim the memory which is used for caching of directory and inode objects. At the default value of vfs_cache_pressure=100 the kernel will attempt to reclaim dentries and inodes at a "fair" rate with respect to pagecache and swapcache reclaim. Decreasing vfs_cache_pressure causes the kernel to prefer to retain dentry and inode caches. When vfs_cache_pressure=0, the kernel will never reclaim dentries and inodes due to memory pressure and this can easily lead to out-of-memory conditions. Increasing vfs_cache_pressure beyond 100 causes the kernel to prefer to reclaim dentries and inodes. Increasing vfs_cache_pressure significantly beyond 100 may have negative performance impact. Reclaim code needs to take various locks to find freeable directory and inode objects. With vfs_cache_pressure=1000, it will look for ten times more freeable objects than there are.
Also we've an article for sysadmins which has a section:
<quote>
With GlusterFS, many users with a lot of storage and many small files easily end up using a lot of RAM on the server side due to 'inode/dentry' caching, leading to decreased performance when the kernel keeps crawling through data-structures on a 40GB RAM system. Changing this value higher than 100 has helped many users to achieve fair caching and more responsiveness from the kernel.
</quote>
Complete article can be found at:
https://gluster.readthedocs.io/en/latest/Administrator%20Guide/Linux%20Kernel%20Tuning/
regards,
On Tue, Sep 5, 2017 at 5:20 PM, Raghavendra Gowdappa <rgowdapp@xxxxxxxxxx> wrote:
+gluster-devel
Ashish just spoke to me about need of GC of inodes due to some state in inode that is being proposed in EC. Hence adding more people to conversation.
> > On 4 September 2017 at 12:34, Csaba Henk <chenk@xxxxxxxxxx> wrote:
> >
> > > I don't know, depends on how sophisticated GC we need/want/can get by. I
> > > guess the complexity will be inherent, ie. that of the algorithm chosen
> > > and
> > > how we address concurrency & performance impacts, but once that's got
> > > right
> > > the other aspects of implementation won't be hard.
> > >
> > > Eg. would it be good just to maintain a simple LRU list?
> > >
>
> Yes. I was also thinking of leveraging lru list. We can invalidate first "n"
> inodes from lru list of fuse inode table.
>
> >
> > That might work for starters.
> >
> > >
> > > Csaba
> > >
> > > On Mon, Sep 4, 2017 at 8:48 AM, Nithya Balachandran <nbalacha@xxxxxxxxxx>
> > > wrote:
> > >
> > >>
> > >>
> > >> On 4 September 2017 at 12:14, Csaba Henk <chenk@xxxxxxxxxx> wrote:
> > >>
> > >>> Basically how I see the fuse invalidate calls as rescuers of sanity.
> > >>>
> > >>> Normally, when you have lot of certain kind of stuff that tends to
> > >>> accumulate, the immediate thought is: let's set up some garbage
> > >>> collection
> > >>> mechanism, that will take care of keeping the accumulation at bay. But
> > >>> that's what doesn't work with inodes in a naive way, as they are
> > >>> referenced
> > >>> from kernel, so we have to keep them around until kernel tells us it's
> > >>> giving up its reference. However, with the fuse invalidate calls we can
> > >>> take the initiative and instruct the kernel: "hey, kernel, give up your
> > >>> references to this thing!"
> > >>>
> > >>> So we are actually free to implement any kind of inode GC in glusterfs,
> > >>> just have to take care to add the proper callback to fuse_invalidate_*
> > >>> and
> > >>> we are good to go.
> > >>>
> > >>>
> > >> That sounds good and something we need to do in the near future. Is this
> > >> something that is easy to implement?
> > >>
> > >>
> > >>> Csaba
> > >>>
> > >>> On Mon, Sep 4, 2017 at 7:00 AM, Nithya Balachandran
> > >>> <nbalacha@xxxxxxxxxx
> > >>> > wrote:
> > >>>
> > >>>>
> > >>>>
> > >>>> On 4 September 2017 at 10:25, Raghavendra Gowdappa
> > >>>> <rgowdapp@xxxxxxxxxx
> > >>>> > wrote:
> > >>>>
> > >>>>>
> > >>>>>
> > >>>>> ----- Original Message -----
> > >>>>> > From: "Nithya Balachandran" <nbalacha@xxxxxxxxxx>
> > >>>>> > Sent: Monday, September 4, 2017 10:19:37 AM
> > >>>>> > Subject: Fuse mounts and inodes
> > >>>>> >
> > >>>>> > Hi,
> > >>>>> >
> > >>>>> > One of the reasons for the memory consumption in gluster fuse
> > >>>>> > mounts
> > >>>>> is the
> > >>>>> > number of inodes in the table which are never kicked out.
> > >>>>> >
> > >>>>> > Is there any way to default to an entry-timeout and
> > >>>>> attribute-timeout value
> > >>>>> > while mounting Gluster using Fuse? Say 60s each so those entries
> > >>>>> will be
> > >>>>> > purged periodically?
> > >>>>>
> > >>>>> Once the entry timeouts, inodes won't be purged. Kernel sends a
> > >>>>> lookup
> > >>>>> to revalidate the mapping of path to inode. AFAIK, reverse
> > >>>>> invalidation
> > >>>>> (see inode_invalidate) is the only way to make kernel forget
> > >>>>> inodes/attributes.
> > >>>>>
> > >>>>> Is that something that can be done from the Fuse mount ? Or is this
> > >>>> something that needs to be added to Fuse?
> > >>>>
> > >>>>> >
> > >>>>> > Regards,
> > >>>>> > Nithya
> > >>>>> >
> > >>>>>
> > >>>>
> > >>>>
> > >>>
> > >>
> > >
> >
>
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Raghavendra G
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