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    SubjectRe: [PATCH v2 2/4] mm/vmalloc: add support for __GFP_NOFAIL
    On Mon, Nov 22, 2021 at 04:32:31PM +0100, Michal Hocko wrote:
    > From: Michal Hocko <mhocko@suse.com>
    >
    > 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 large part of the vmalloc implementation already complies with the
    > 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@suse.com>
    > ---
    > mm/vmalloc.c | 22 +++++++++++++++++-----
    > 1 file changed, 17 insertions(+), 5 deletions(-)
    >
    > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
    > index 17ca7001de1f..b6aed4f94a85 100644
    > --- a/mm/vmalloc.c
    > +++ b/mm/vmalloc.c
    > @@ -2844,6 +2844,8 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
    > * more permissive.
    > */
    > if (!order) {
    > + gfp_t bulk_gfp = gfp & ~__GFP_NOFAIL;
    > +
    > while (nr_allocated < nr_pages) {
    > unsigned int nr, nr_pages_request;
    >
    > @@ -2861,12 +2863,12 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
    > * but mempolcy want to alloc memory by interleaving.
    > */
    > if (IS_ENABLED(CONFIG_NUMA) && nid == NUMA_NO_NODE)
    > - nr = alloc_pages_bulk_array_mempolicy(gfp,
    > + nr = alloc_pages_bulk_array_mempolicy(bulk_gfp,
    > nr_pages_request,
    > pages + nr_allocated);
    >
    > else
    > - nr = alloc_pages_bulk_array_node(gfp, nid,
    > + nr = alloc_pages_bulk_array_node(bulk_gfp, nid,
    > nr_pages_request,
    > pages + nr_allocated);
    >
    > @@ -2921,6 +2923,7 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
    > {
    > const gfp_t nested_gfp = (gfp_mask & GFP_RECLAIM_MASK) | __GFP_ZERO;
    > const gfp_t orig_gfp_mask = gfp_mask;
    > + bool nofail = gfp_mask & __GFP_NOFAIL;
    > unsigned long addr = (unsigned long)area->addr;
    > unsigned long size = get_vm_area_size(area);
    > unsigned long array_size;
    > @@ -2978,8 +2981,12 @@ 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 (nofail && (ret < 0))
    > + schedule_timeout_uninterruptible(1);
    > + } while (nofail && (ret < 0));
    >
    > if ((gfp_mask & (__GFP_FS | __GFP_IO)) == __GFP_IO)
    > memalloc_nofs_restore(flags);
    > @@ -3074,9 +3081,14 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
    > VM_UNINITIALIZED | vm_flags, start, end, node,
    > gfp_mask, caller);
    > if (!area) {
    > + bool nofail = gfp_mask & __GFP_NOFAIL;
    > warn_alloc(gfp_mask, NULL,
    > - "vmalloc error: size %lu, vm_struct allocation failed",
    > - real_size);
    > + "vmalloc error: size %lu, vm_struct allocation failed%s",
    > + real_size, (nofail) ? ". Retrying." : "");
    > + if (nofail) {
    > + schedule_timeout_uninterruptible(1);
    > + goto again;
    > + }
    > goto fail;
    > }
    >
    > --
    > 2.30.2
    >
    I have raised two concerns in our previous discussion about this change,
    well that is sad...

    --
    Vlad Rezki

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