linux-kernel - Re: [PATCH v6 01/12] mm/vmalloc: fix vmalloc_to

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Message-Id: <20200821130757.289570e4bb491672087d3396@linux-foundation.org>
Date:   Fri, 21 Aug 2020 13:07:57 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Nicholas Piggin <npiggin@...il.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        Zefan Li <lizefan@...wei.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Christoph Hellwig <hch@...radead.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>
Subject: Re: [PATCH v6 01/12] mm/vmalloc: fix vmalloc_to_page for huge vmap
 mappings

On Sat, 22 Aug 2020 01:12:05 +1000 Nicholas Piggin <npiggin@...il.com> wrote:

> vmalloc_to_page returns NULL for addresses mapped by larger pages[*].
> Whether or not a vmap is huge depends on the architecture details,
> alignments, boot options, etc., which the caller can not be expected
> to know. Therefore HUGE_VMAP is a regression for vmalloc_to_page.

I assume this doesn't matter in current mainline?

If wrong, then what are the user-visible effects and why no cc:stable?

> This change teaches vmalloc_to_page about larger pages, and returns
> the struct page that corresponds to the offset within the large page.
> This makes the API agnostic to mapping implementation details.