Re: [PATCH 3/3] xfile: implement write caching

Christoph Hellwig
2024-01-04T06:20:34Z

On Wed, Jan 03, 2024 at 05:33:56PM -0800, Darrick J. Wong wrote:
> Sort of both. For xfbtrees (or anything mapping a xfs_buftarg atop an
> xfile) we can't use the cheap(er) kmap_local_page and have to use kmap,
> which ... is expensive, isn't it?

A little, but not really enough to explain the numbers you quoted..

> Granted, forbidding highmem like you posted today makes all of this
> /much/ simpler so I think it's probably worth the increased chances of
> ENOMEM on i386.
>
> That said, why not avoid a trip through shmem_get_folio_gfp aka
> filemap_get_entry if we can? Even if we can use page_address directly
> now?

Sure, I just suspect the commit message is wrong and it's not about
mapping the page into the kernel address space but something else.