Re: [RFC PATCH v2] NFSD: Add asynchronous write throttling support for UNSTABLE WRITEs

[Chuck Lever <cel@kernel.org>]

On 1/11/26 11:15 PM, NeilBrown wrote:
>>> What exactly is "the memory problem"?  Do you have specific symptoms you
>>> are trying to address?  Have you had NFS server run out of memory and
>>> grind to a halt?
>> Review the past 9 months of Mike's work on direct I/O, published on
>> this mailing list. Hammerspace has measured this misbehavior and
>> experienced server melt-down. Their solution is to avoid using the
>> page cache entirely.
> I didn't pay very close attention but I thought the assessment was that
> adding lots of single-use pages to the page cache, and then having to
> clean them out later, caused a lot of unnecessary work that was best
> avoided, and that drop-behind addressed this.

Drop-behind is too inefficient to be used here. This is why direct I/O
is also an option. Direct I/O is measurably superior to drop-behind.


> Are you trying to find another way to address the same problem?

Yes. I don't think we can backport direct I/O, for example, to LTS
kernels. I expect it will be important to have an alternative to the
new I/O caching modes for this reason alone.


-- 
Chuck Lever