Re: [PATCH v2 4/5] mm/mremap: restore VMA_ACCOUNT_BIT if the unmap fails

["Jose A. Perez de Azpillaga" <azpijr@gmail.com>]

On 11/3/26 12:46 AM, Josef Bacik wrote:
> If the unmap at the end of an mremap() move fails, the source VMA stays
> without VMA_ACCOUNT_BIT. Neither munmap() nor exit_mmap() uncharges it
> then, so the charge for all of its pages stays in vm_committed_as after
> the process is gone.
> 
> unmap_source_vma() clears the flag on the whole source VMA before the unmap
> and sets it again on the remaining parts afterwards, but its error path
> returns without doing so.
> 
> This was reproduced with fault injection: each failure on an anonymous
> mapping left Committed_AS higher by the size of the whole VMA after
> everything was unmapped.
> 
> Fix by setting the flag again on everything in the range of the original
> VMA, on both paths, with a new helper. A failed unmap may have split the
> VMA already, so the helper walks the range.
> 
> Fixes: 51df7bcb6151 ("mm/mremap: account memory on do_munmap() failure")
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>

nice!

Reviewed-by: Jose A. Perez de Azpillaga <azpijr@gmail.com>

-- 
cheers,
jose a. p-a