On Sat, Jun 14, 2025 at 5:25 AM Klara Modin klarasmodin@gmail.com wrote:
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 ziy@nvidia.com Co-developed-by: Rafael Aquini raquini@redhat.com Signed-off-by: Rafael Aquini raquini@redhat.com Signed-off-by: Nico Pache npache@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.
Thanks Klara-- I will make sure to add it on the next version!
} 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