linux-kernel - [PATCH RFC 2/3] mm/vmalloc.c: add flags to mark vm_map

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Date:   Wed,  9 Nov 2022 11:35:33 +0800
From:   Baoquan He <bhe@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.org,
        stephen.s.brennan@...cle.com, urezki@...il.com, hch@...radead.org,
        Baoquan He <bhe@...hat.com>
Subject: [PATCH RFC 2/3] mm/vmalloc.c: add flags to mark vm_map_ram area

Through vmalloc API, a virtual kernel area is reserved for physical
address mapping. And vmap_area is used to track them, and vm_struct is
allocated to associate with the vmap_area to store more information and
passed out.

However, area reserved via vm_map_ram() is an exception. It doesn't have
vm_struct to associate with vmap_area. And we can't simply recognize the
vm_map_ram areas with '->vm == NULL' because the normal freeing path will
set va->vm = NULL before unmapping, please see function remove_vm_area().

Meanwhile, there are two types of vm_map_ram area. One is the whole
vmap_area being reserved and mapped at one time; the other is the
whole vmap_area with VMAP_BLOCK_SIZE size being reserved, while mapped
into split regions with smaller size several times.

To mark the area reserved through vm_map_ram(), add flags into the
union field of struct vmap_area to reuse the space since that union
space is free anyway if it's vm_map_ram area.

This is a preparatoin for later use.

Signed-off-by: Baoquan He <bhe@...hat.com>
---
 include/linux/vmalloc.h |  1 +
 mm/vmalloc.c            | 17 ++++++++++++++++-
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
index 096d48aa3437..b739a60b73da 100644
--- a/include/linux/vmalloc.h
+++ b/include/linux/vmalloc.h
@@ -75,6 +75,7 @@ struct vmap_area {
 	union {
 		unsigned long subtree_max_size; /* in "free" tree */
 		struct vm_struct *vm;           /* in "busy" tree */
+		unsigned long flags; /* mark type of vm_map_ram area */
 	};
 };
 
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 5d3fd3e6fe09..41d82dc07e13 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1815,6 +1815,7 @@ static void free_vmap_area_noflush(struct vmap_area *va)
 
 	spin_lock(&vmap_area_lock);
 	unlink_va(va, &vmap_area_root);
+	va->flags = 0;
 	spin_unlock(&vmap_area_lock);
 
 	nr_lazy = atomic_long_add_return((va->va_end - va->va_start) >>
@@ -1887,6 +1888,9 @@ struct vmap_area *find_vmap_area(unsigned long addr)
 
 #define VMAP_BLOCK_SIZE		(VMAP_BBMAP_BITS * PAGE_SIZE)
 
+#define VMAP_RAM	0x1
+#define VMAP_BLOCK	0x2
+
 struct vmap_block_queue {
 	spinlock_t lock;
 	struct list_head free;
@@ -1967,6 +1971,9 @@ static void *new_vmap_block(unsigned int order, gfp_t gfp_mask)
 		kfree(vb);
 		return ERR_CAST(va);
 	}
+	spin_lock(&vmap_area_lock);
+	va->flags = VMAP_RAM|VMAP_BLOCK;
+	spin_unlock(&vmap_area_lock);
 
 	vaddr = vmap_block_vaddr(va->va_start, 0);
 	spin_lock_init(&vb->lock);
@@ -2229,8 +2236,12 @@ void vm_unmap_ram(const void *mem, unsigned int count)
 		return;
 	}
 
-	va = find_vmap_area(addr);
+	spin_lock(&vmap_area_lock);
+	va = __find_vmap_area((unsigned long)addr, &vmap_area_root);
 	BUG_ON(!va);
+	if (va)
+		va->flags &= ~VMAP_RAM;
+	spin_unlock(&vmap_area_lock);
 	debug_check_no_locks_freed((void *)va->va_start,
 				    (va->va_end - va->va_start));
 	free_unmap_vmap_area(va);
@@ -2269,6 +2280,10 @@ void *vm_map_ram(struct page **pages, unsigned int count, int node)
 		if (IS_ERR(va))
 			return NULL;
 
+		spin_lock(&vmap_area_lock);
+		va->flags = VMAP_RAM;
+		spin_unlock(&vmap_area_lock);
+
 		addr = va->va_start;
 		mem = (void *)addr;
 	}
-- 
2.34.1