On 2022/7/8 13:36, Naoya Horiguchi wrote:
> From: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
>
> I found a weird state of 1GB hugepage pool, caused by the following
> procedure:
>
> - run a process reserving all free 1GB hugepages,
> - shrink free 1GB hugepage pool to zero (i.e. writing 0 to
> /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages), then
> - kill the reserving process.
>
> , then all the hugepages are free *and* surplus at the same time.
>
> $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages
> 3
> $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/free_hugepages
> 3
> $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/resv_hugepages
> 0
> $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/surplus_hugepages
> 3
>
> This state is resolved by reserving and allocating the pages then
> freeing them again, so this seems not to result in serious problem.
> But it's a little surprising (shrinking pool suddenly fails).
>
> This behavior is caused by hstate_is_gigantic() check in
> return_unused_surplus_pages(). This was introduced so long ago in 2008
> by commit aa888a74977a ("hugetlb: support larger than MAX_ORDER"), and
> at that time the gigantic pages were not supposed to be allocated/freed
> at run-time. Now kernel can support runtime allocation/free, so let's
> check gigantic_page_runtime_supported() together.
>
> Signed-off-by: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
Looks good to me. Thanks.
Reviewed-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
