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Message-Id: <20240322121912.3bc9e58cfda1b7c92aac9c4f@linux-foundation.org>
Date: Fri, 22 Mar 2024 12:19:12 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Dev Jain <dev.jain@....com>
Cc: shuah@...nel.org, linux-mm@...ck.org, linux-kselftest@...r.kernel.org,
linux-kernel@...r.kernel.org, Anshuman.Khandual@....com
Subject: Re: [PATCH] selftests/mm: Confirm VA exhaustion without reliance on
correctness of mmap()
On Fri, 22 Mar 2024 10:42:47 +0530 Dev Jain <dev.jain@....com> wrote:
>
> On 3/22/24 03:21, Andrew Morton wrote:
> > On Thu, 21 Mar 2024 16:05:22 +0530 Dev Jain <dev.jain@....com> wrote:
> >
> >> Currently, VA exhaustion is being checked by passing a hint to mmap() and
> >> expecting it to fail. This patch makes a stricter test by successful write()
> >> calls from /proc/self/maps to a dump file, confirming that a free chunk is
> >> indeed not available.
> > What's wrong with the current approach?
> While populating the lower VA space, mmap() fails because we have
> exhausted the space.
>
> Then, in validate_lower_address_hint(), because mmap() fails, we confirm
> that we have
>
> indeed exhausted the space. There is a circular logic involved here.
>
> Assume that there is a bug in mmap(), also assume that it exists
> independent of whether
>
> you pass a hint address or not; that for some reason it is not able to
> find a 1GB chunk.
>
> My idea is to assert the exhaustion against some other method.
Thanks. I added the above to the changelog.
>
> Also, in the following line in validate_complete_va_space():
>
> if (start_addr - prev_end_addr >= SZ_1GB)
>
> I made a small error, I forgot to use MAP_CHUNK_SIZE instead of SZ_1GB.
And the preceding comment might need an edit. Please send an updated
patch?
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