Re: [PATCH v3 6/7] mm: truncate: split huge page cache page to a non-zero order if possible.

[Hugh Dickins <hughd@google.com>]

On Mon, 17 Apr 2023, Zi Yan wrote:
> 
> What do you think? If you have a better idea, I am all ears. And if you
> are willing to help me review the more complicated code changes, I am
> more than happy to implement it in the next version. :)

Sorry, no, not me.  You'll have to persuade someone else that "optimizing"
truncation is a worthwhile path to pursue (and to pursue now) - I was just
trying to illustrate that the current patchset didn't seem very useful.

But don't throw your work away.  I expect some of it can become useful
later e.g. once most of the main filesystems support large folios, and
the complication of CONFIG_READ_ONLY_THP_FOR_FS can be deleted.

I doubt my "minimizing the number of folios" approach would be worth
the effort; I think more likely that we shall settle on an intermediate
folio size (between 4K and THP: maybe 64K, but not necessarily the same
on all machines or all workloads) to aim for, and then maybe truncation
of THP would split to those units.  But it's not a job I shall get into
- I'll just continue to report and try to fix what bugs I see.

Hugh