mm/huge_memory: convert "tva_flags" to "enum tva_type"

When determining which THP orders are eligible for a VMA mapping, we have
previously specified tva_flags, however it turns out it is really not
necessary to treat these as flags.

Rather, we distinguish between distinct modes.

The only case where we previously combined flags was with
TVA_ENFORCE_SYSFS, but we can avoid this by observing that this is the
default, except for MADV_COLLAPSE or an edge cases in
collapse_pte_mapped_thp() and hugepage_vma_revalidate(), and adding a mode
specifically for this case - TVA_FORCED_COLLAPSE.

We have:
* smaps handling for showing "THPeligible"
* Pagefault handling
* khugepaged handling
* Forced collapse handling: primarily MADV_COLLAPSE, but also for
  an edge case in collapse_pte_mapped_thp()

Disregarding the edge cases, we only want to ignore sysfs settings only
when we are forcing a collapse through MADV_COLLAPSE, otherwise we want to
enforce it, hence this patch does the following flag to enum conversions:

* TVA_SMAPS | TVA_ENFORCE_SYSFS -> TVA_SMAPS
* TVA_IN_PF | TVA_ENFORCE_SYSFS -> TVA_PAGEFAULT
* TVA_ENFORCE_SYSFS             -> TVA_KHUGEPAGED
* 0                             -> TVA_FORCED_COLLAPSE

With this change, we immediately know if we are in the forced collapse
case, which will be valuable next.

Link: https://lkml.kernel.org/r/20250815135549.130506-3-usamaarif642@gmail.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Usama Arif <usamaarif642@gmail.com>
Acked-by: Usama Arif <usamaarif642@gmail.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Barry Song <baohua@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Jann Horn <jannh@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Mariano Pache <npache@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yafang <laoar.shao@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 18 insertions, 12 deletions

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 22b8b067b295..92ea0b9771fa 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -94,12 +94,15 @@ extern struct kobj_attribute thpsize_shmem_enabled_attr;
 #define THP_ORDERS_ALL	\
 	(THP_ORDERS_ALL_ANON | THP_ORDERS_ALL_SPECIAL | THP_ORDERS_ALL_FILE_DEFAULT)
 
-#define TVA_SMAPS		(1 << 0)	/* Will be used for procfs */
-#define TVA_IN_PF		(1 << 1)	/* Page fault handler */
-#define TVA_ENFORCE_SYSFS	(1 << 2)	/* Obey sysfs configuration */
+enum tva_type {
+	TVA_SMAPS,		/* Exposing "THPeligible:" in smaps. */
+	TVA_PAGEFAULT,		/* Serving a page fault. */
+	TVA_KHUGEPAGED,		/* Khugepaged collapse. */
+	TVA_FORCED_COLLAPSE,	/* Forced collapse (e.g. MADV_COLLAPSE). */
+};
 
-#define thp_vma_allowable_order(vma, vm_flags, tva_flags, order) \
-	(!!thp_vma_allowable_orders(vma, vm_flags, tva_flags, BIT(order)))
+#define thp_vma_allowable_order(vma, vm_flags, type, order) \
+	(!!thp_vma_allowable_orders(vma, vm_flags, type, BIT(order)))
 
 #define split_folio(f) split_folio_to_list(f, NULL)
 
@@ -264,14 +267,14 @@ static inline unsigned long thp_vma_suitable_orders(struct vm_area_struct *vma,
 
 unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma,
 					 vm_flags_t vm_flags,
-					 unsigned long tva_flags,
+					 enum tva_type type,
 					 unsigned long orders);
 
 /**
  * thp_vma_allowable_orders - determine hugepage orders that are allowed for vma
  * @vma:  the vm area to check
  * @vm_flags: use these vm_flags instead of vma->vm_flags
- * @tva_flags: Which TVA flags to honour
+ * @type: TVA type
  * @orders: bitfield of all orders to consider
  *
  * Calculates the intersection of the requested hugepage orders and the allowed
@@ -285,11 +288,14 @@ unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma,
 static inline
 unsigned long thp_vma_allowable_orders(struct vm_area_struct *vma,
 				       vm_flags_t vm_flags,
-				       unsigned long tva_flags,
+				       enum tva_type type,
 				       unsigned long orders)
 {
-	/* Optimization to check if required orders are enabled early. */
-	if ((tva_flags & TVA_ENFORCE_SYSFS) && vma_is_anonymous(vma)) {
+	/*
+	 * Optimization to check if required orders are enabled early. Only
+	 * forced collapse ignores sysfs configs.
+	 */
+	if (type != TVA_FORCED_COLLAPSE && vma_is_anonymous(vma)) {
 		unsigned long mask = READ_ONCE(huge_anon_orders_always);
 
 		if (vm_flags & VM_HUGEPAGE)
@@ -303,7 +309,7 @@ unsigned long thp_vma_allowable_orders(struct vm_area_struct *vma,
 			return 0;
 	}
 
-	return __thp_vma_allowable_orders(vma, vm_flags, tva_flags, orders);
+	return __thp_vma_allowable_orders(vma, vm_flags, type, orders);
 }
 
 struct thpsize {
@@ -547,7 +553,7 @@ static inline unsigned long thp_vma_suitable_orders(struct vm_area_struct *vma,
 
 static inline unsigned long thp_vma_allowable_orders(struct vm_area_struct *vma,
 					vm_flags_t vm_flags,
-					unsigned long tva_flags,
+					enum tva_type type,
 					unsigned long orders)
 {
 	return 0;