linux-kernel - Re: [RFC PATCH v3 0/4] Support large folios for tmpfs

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Message-ID: <5p22lehyjjzxvohppdmt2vkkplrrd6ss6tev2px6troxyii4ab@eaphjvxiwrfc>
Date: Tue, 22 Oct 2024 13:06:22 +0300
From: "Kirill A. Shutemov" <kirill@...temov.name>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc: Matthew Wilcox <willy@...radead.org>, akpm@...ux-foundation.org, 
	hughd@...gle.com, david@...hat.com, wangkefeng.wang@...wei.com, 21cnbao@...il.com, 
	ryan.roberts@....com, ioworker0@...il.com, da.gomez@...sung.com, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [RFC PATCH v3 0/4] Support large folios for tmpfs

On Tue, Oct 22, 2024 at 11:34:14AM +0800, Baolin Wang wrote:
> IIUC, most file systems use method similar to iomap buffered IO (see
> iomap_get_folio()) to allocate huge pages. What I mean is that, it would be
> better to have a real use case to add a hint for allocating THP (other than
> tmpfs).

I would be nice to hear from folks who works with production what the
actual needs are.

But I find asymmetry between MADV_ hints and FADV_ hints wrt huge pages
not justified. I think it would be easy to find use-cases for
FADV_HUGEPAGE/FADV_NOHUGEPAGE.

Furthermore I think it would be useful to have some kind of mechanism to
make these hints persistent: any open of a file would have these hints set
by default based on inode metadata on backing storage. Although, I am not
sure what the right way to archive that. xattrs?

-- 
  Kiryl Shutsemau / Kirill A. Shutemov