On Tue, 26 Oct 2021, Michal Hocko wrote:
> From: Michal Hocko <mhocko@xxxxxxxx>
>
> Dave Chinner has mentioned that some of the xfs code would benefit from
> kvmalloc support for __GFP_NOFAIL because they have allocations that
> cannot fail and they do not fit into a single page.
>
> The larg part of the vmalloc implementation already complies with the
*large*
> given gfp flags so there is no work for those to be done. The area
> and page table allocations are an exception to that. Implement a retry
> loop for those.
>
> Add a short sleep before retrying. 1 jiffy is a completely random
> timeout. Ideally the retry would wait for an explicit event - e.g.
> a change to the vmalloc space change if the failure was caused by
> the space fragmentation or depletion. But there are multiple different
> reasons to retry and this could become much more complex. Keep the retry
> simple for now and just sleep to prevent from hogging CPUs.
>
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> mm/vmalloc.c | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index c6cc77d2f366..602649919a9d 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2941,8 +2941,12 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
> else if ((gfp_mask & (__GFP_FS | __GFP_IO)) == 0)
> flags = memalloc_noio_save();
>
> - ret = vmap_pages_range(addr, addr + size, prot, area->pages,
> + do {
> + ret = vmap_pages_range(addr, addr + size, prot, area->pages,
> page_shift);
> + if (ret < 0)
> + schedule_timeout_uninterruptible(1);
> + } while ((gfp_mask & __GFP_NOFAIL) && (ret < 0));
>
> if ((gfp_mask & (__GFP_FS | __GFP_IO)) == __GFP_IO)
> memalloc_nofs_restore(flags);
> @@ -3032,6 +3036,10 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
> warn_alloc(gfp_mask, NULL,
> "vmalloc error: size %lu, vm_struct allocation failed",
> real_size);
> + if (gfp_mask & __GFP_NOFAIL) {
> + schedule_timeout_uninterruptible(1);
> + goto again;
> + }
Shouldn't the retry happen *before* the warning?
NeilBrown
> goto fail;
> }
>
> --
> 2.30.2
>
>
