linux-ext4 - Re: [PATCH 02/10] ext2: Convert ext2_check_page to ext2_check

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Date:   Tue, 3 Oct 2023 13:02:54 +0200
From:   Jan Kara <jack@...e.cz>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc:     Jan Kara <jack@...e.com>, linux-ext4@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        "Fabio M . De Francesco" <fmdefrancesco@...il.com>
Subject: Re: [PATCH 02/10] ext2: Convert ext2_check_page to ext2_check_folio

On Thu 21-09-23 21:07:39, Matthew Wilcox (Oracle) wrote:
> Support in this function for large folios is limited to supporting
> filesystems with block size > PAGE_SIZE.  This new functionality will only
> be supported on machines without HIGHMEM, so the problem of kmap_local
> only being able to map a single page in the folio can be ignored.
> We will not use large folios for ext2 directories on HIGHMEM machines.

A look like a fool replying to the same patch multiple times ;) but how is
this supposed to work even without HIGHMEM? Suppose we have a page size 4k
and block size 16k. Directory entries in a block can then straddle 4k
boundary so if kmap_local() is mapping only a single page, then we are
going to have hard time parsing this all?

Oh, I guess you are pointing to the fact kmap_local_folio() gives you back
address usable for the whole folio access if !HIGHMEM. But then all the
iterations (e.g. in ext2_readdir()) has to be folio-size based and not
page-size based as they currently are? You didn't change these iterations
in your patches which has confused me...

								Honza 

-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR