[U-Boot] malloc: improve memalign fragmentation fix

[Tom Rini]

On Mon, Apr 25, 2016 at 03:55:42PM -0600, Stephen Warren wrote:

> From: Stephen Warren <swarren at nvidia.com>
> 
> Commit 4f144a416469 "malloc: work around some memalign fragmentation
> issues" enhanced memalign() so that it can succeed in more cases where
> heap fragmentation is present. However, it did not solve as many cases
> as it could. This patch enhances the code to cover more cases.
> 
> The alignment code works by allocating more space than the user requests,
> then adjusting the returned pointer to achieve alignment. In general, one
> must allocate "alignment" bytes more than the user requested in order to
> guarantee that alignment is possible. This is what the original code does.
> The previous enhancement attempted a second allocation if the padded
> allocation failed, and succeeded if that allocation just happened to be
> aligned; a fluke that happened often in practice. There are still cases
> where this could fail, yet where it is still possible to honor the user's
> allocation request. In particular, if the heap contains a free region that
> is large enough for the user's request, and for leading padding to ensure
> alignment, but has no or little space for any trailing padding. In this
> case, we can make a third(!) allocation attempt after calculating exactly
> the size of the leading padding required to achieve alignment, which is
> the minimal over-allocation needed for the overall memalign() operation to
> succeed if the third and second allocations end up at the same location.
> 
> This patch isn't checkpatch-clean, since it conforms to the existing
> coding style in dlmalloc.c, which is different to the rest of U-Boot.
> 
> Signed-off-by: Stephen Warren <swarren at nvidia.com>
> Reviewed-by: Tom Rini <trini at konsulko.com>

Applied to u-boot/master, thanks!

-- 
Tom
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