Hi,
On 2025-05-14 21:38:54 -0600, Nico Pache wrote:
> setting /transparent_hugepages/enabled=always allows applications
> to benefit from THPs without having to madvise. However, the page fault
> handler takes very few considerations to decide weather or not to actually
> use a THP. This can lead to a lot of wasted memory. khugepaged only
> operates on memory that was either allocated with enabled=always or
> MADV_HUGEPAGE.
>
> Introduce the ability to set enabled=defer, which will prevent THPs from
> being allocated by the page fault handler unless madvise is set,
> leaving it up to khugepaged to decide which allocations will collapse to a
> THP. This should allow applications to benefits from THPs, while curbing
> some of the memory waste.
>
> Acked-by: Zi Yan <z...@nvidia.com>
> Co-developed-by: Rafael Aquini <raqu...@redhat.com>
> Signed-off-by: Rafael Aquini <raqu...@redhat.com>
> Signed-off-by: Nico Pache <npa...@redhat.com>
...
> @@ -315,13 +318,20 @@ static ssize_t enabled_store(struct kobject *kobj,
>
> if (sysfs_streq(buf, "always")) {
> clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
> &transparent_hugepage_flags);
> + clear_bit(TRANSPARENT_HUGEPAGE_DEFER_PF_FLAG,
> &transparent_hugepage_flags);
> set_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags);
> + } else if (sysfs_streq(buf, "defer")) {
> + clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
> &transparent_hugepage_flags);
> + clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
> &transparent_hugepage_flags);
> + set_bit(TRANSPARENT_HUGEPAGE_DEFER_PF_FLAG,
> &transparent_hugepage_flags);
> } else if (sysfs_streq(buf, "madvise")) {
> clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
> &transparent_hugepage_flags);
> + clear_bit(TRANSPARENT_HUGEPAGE_DEFER_PF_FLAG,
> &transparent_hugepage_flags);
> set_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
> &transparent_hugepage_flags);
> } else if (sysfs_streq(buf, "never")) {
> clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
> &transparent_hugepage_flags);
> clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
> &transparent_hugepage_flags);
> + clear_bit(TRANSPARENT_HUGEPAGE_DEFER_PF_FLAG,
> &transparent_hugepage_flags);
> } else
> ret = -EINVAL;
>
> @@ -954,18 +964,31 @@ static int __init setup_transparent_hugepage(char *str)
> &transparent_hugepage_flags);
> clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
> &transparent_hugepage_flags);
> + clear_bit(TRANSPARENT_HUGEPAGE_DEFER_PF_FLAG,
> + &transparent_hugepage_flags);
> ret = 1;
> + } else if (!strcmp(str, "defer")) {
> + clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
> + &transparent_hugepage_flags);
> + clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
> + &transparent_hugepage_flags);
> + set_bit(TRANSPARENT_HUGEPAGE_DEFER_PF_FLAG,
> + &transparent_hugepage_flags);
There should probably be a corresponding
ret = 1;
here. Otherwise the cannot parse message will displayed even if defer
was set.
> } else if (!strcmp(str, "madvise")) {
> clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
> &transparent_hugepage_flags);
> + clear_bit(TRANSPARENT_HUGEPAGE_DEFER_PF_FLAG,
> + &transparent_hugepage_flags);
> set_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
> - &transparent_hugepage_flags);
> + &transparent_hugepage_flags);
> ret = 1;
> } else if (!strcmp(str, "never")) {
> clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
> &transparent_hugepage_flags);
> clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
> &transparent_hugepage_flags);
> + clear_bit(TRANSPARENT_HUGEPAGE_DEFER_PF_FLAG,
> + &transparent_hugepage_flags);
> ret = 1;
> }
> out:
> --
> 2.49.0
>
Regards,
Klara Modin
