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Message-ID: <20250725162258.1043176-4-usamaarif642@gmail.com>
Date: Fri, 25 Jul 2025 17:22:42 +0100
From: Usama Arif <usamaarif642@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>,
david@...hat.com,
linux-mm@...ck.org
Cc: linux-fsdevel@...r.kernel.org,
corbet@....net,
rppt@...nel.org,
surenb@...gle.com,
mhocko@...e.com,
hannes@...xchg.org,
baohua@...nel.org,
shakeel.butt@...ux.dev,
riel@...riel.com,
ziy@...dia.com,
laoar.shao@...il.com,
dev.jain@....com,
baolin.wang@...ux.alibaba.com,
npache@...hat.com,
lorenzo.stoakes@...cle.com,
Liam.Howlett@...cle.com,
ryan.roberts@....com,
vbabka@...e.cz,
jannh@...gle.com,
Arnd Bergmann <arnd@...db.de>,
sj@...nel.org,
linux-kernel@...r.kernel.org,
linux-doc@...r.kernel.org,
kernel-team@...a.com,
Usama Arif <usamaarif642@...il.com>
Subject: [PATCH 3/5] mm/huge_memory: treat MADV_COLLAPSE as an advise with PR_THP_DISABLE_EXCEPT_ADVISED
From: David Hildenbrand <david@...hat.com>
Let's allow for making MADV_COLLAPSE succeed on areas that neither have
VM_HUGEPAGE nor VM_NOHUGEPAGE when we have THP disabled
unless explicitly advised (PR_THP_DISABLE_EXCEPT_ADVISED).
MADV_COLLAPSE is a clear advise that we want to collapse.
Note that we still respect the VM_NOHUGEPAGE flag, just like
MADV_COLLAPSE always does. So consequently, MADV_COLLAPSE is now only
refused on VM_NOHUGEPAGE with PR_THP_DISABLE_EXCEPT_ADVISED.
Co-developed-by: Usama Arif <usamaarif642@...il.com>
Signed-off-by: Usama Arif <usamaarif642@...il.com>
Signed-off-by: David Hildenbrand <david@...hat.com>
---
include/linux/huge_mm.h | 8 +++++++-
include/uapi/linux/prctl.h | 2 +-
mm/huge_memory.c | 5 +++--
mm/memory.c | 6 ++++--
mm/shmem.c | 2 +-
5 files changed, 16 insertions(+), 7 deletions(-)
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index b0ff54eee81c..aeaf93f8ac2e 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -329,7 +329,7 @@ struct thpsize {
* through madvise or prctl.
*/
static inline bool vma_thp_disabled(struct vm_area_struct *vma,
- vm_flags_t vm_flags)
+ vm_flags_t vm_flags, bool forced_collapse)
{
/* Are THPs disabled for this VMA? */
if (vm_flags & VM_NOHUGEPAGE)
@@ -343,6 +343,12 @@ static inline bool vma_thp_disabled(struct vm_area_struct *vma,
*/
if (vm_flags & VM_HUGEPAGE)
return false;
+ /*
+ * Forcing a collapse (e.g., madv_collapse), is a clear advise to
+ * use THPs.
+ */
+ if (forced_collapse)
+ return false;
return test_bit(MMF_DISABLE_THP_EXCEPT_ADVISED, &vma->vm_mm->flags);
}
diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
index 9c1d6e49b8a9..ee4165738779 100644
--- a/include/uapi/linux/prctl.h
+++ b/include/uapi/linux/prctl.h
@@ -185,7 +185,7 @@ struct prctl_mm_map {
#define PR_SET_THP_DISABLE 41
/*
* Don't disable THPs when explicitly advised (e.g., MADV_HUGEPAGE /
- * VM_HUGEPAGE).
+ * VM_HUGEPAGE / MADV_COLLAPSE).
*/
# define PR_THP_DISABLE_EXCEPT_ADVISED (1 << 1)
#define PR_GET_THP_DISABLE 42
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 85252b468f80..ef5ccb0ec5d5 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -104,7 +104,8 @@ unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma,
{
const bool smaps = type == TVA_SMAPS;
const bool in_pf = type == TVA_PAGEFAULT;
- const bool enforce_sysfs = type != TVA_FORCED_COLLAPSE;
+ const bool forced_collapse = type == TVA_FORCED_COLLAPSE;
+ const bool enforce_sysfs = !forced_collapse;
unsigned long supported_orders;
/* Check the intersection of requested and supported orders. */
@@ -122,7 +123,7 @@ unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma,
if (!vma->vm_mm) /* vdso */
return 0;
- if (thp_disabled_by_hw() || vma_thp_disabled(vma, vm_flags))
+ if (thp_disabled_by_hw() || vma_thp_disabled(vma, vm_flags, forced_collapse))
return 0;
/* khugepaged doesn't collapse DAX vma, but page fault is fine. */
diff --git a/mm/memory.c b/mm/memory.c
index be761753f240..bd04212d6f79 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5186,9 +5186,11 @@ vm_fault_t do_set_pmd(struct vm_fault *vmf, struct folio *folio, struct page *pa
* It is too late to allocate a small folio, we already have a large
* folio in the pagecache: especially s390 KVM cannot tolerate any
* PMD mappings, but PTE-mapped THP are fine. So let's simply refuse any
- * PMD mappings if THPs are disabled.
+ * PMD mappings if THPs are disabled. As we already have a THP ...
+ * behave as if we are forcing a collapse.
*/
- if (thp_disabled_by_hw() || vma_thp_disabled(vma, vma->vm_flags))
+ if (thp_disabled_by_hw() || vma_thp_disabled(vma, vma->vm_flags,
+ /* forced_collapse=*/ true))
return ret;
if (!thp_vma_suitable_order(vma, haddr, PMD_ORDER))
diff --git a/mm/shmem.c b/mm/shmem.c
index e6cdfda08aed..30609197a266 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1816,7 +1816,7 @@ unsigned long shmem_allowable_huge_orders(struct inode *inode,
vm_flags_t vm_flags = vma ? vma->vm_flags : 0;
unsigned int global_orders;
- if (thp_disabled_by_hw() || (vma && vma_thp_disabled(vma, vm_flags)))
+ if (thp_disabled_by_hw() || (vma && vma_thp_disabled(vma, vm_flags, shmem_huge_force)))
return 0;
global_orders = shmem_huge_global_enabled(inode, index, write_end,
--
2.47.3
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