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    SubjectRe: [PATCH v1 2/7] mm/vmalloc.c: add flags to mark vm_map_ram area
    On Wed, Dec 07, 2022 at 04:03:41PM +0800, Baoquan He wrote:
    > On 12/05/22 at 01:56pm, Uladzislau Rezki wrote:
    > > > Through vmalloc API, a virtual kernel area is reserved for physical
    > > > address mapping. And vmap_area is used to track them, while 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 recognize the
    > > > vmap_area with '->vm == NULL' as a vm_map_ram() area 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 via vb_alloc().
    > > >
    > > > To mark the area reserved through vm_map_ram(), add flags field into
    > > > struct vmap_area. Bit 0 indicates whether it's a vm_map_ram area,
    > > > while bit 1 indicates whether it's a vmap_block type of vm_map_ram
    > > > area.
    > > >
    > > > This is a preparatoin for later use.
    > > >
    > > > Signed-off-by: Baoquan He <bhe@redhat.com>
    > > > ---
    > > > include/linux/vmalloc.h | 1 +
    > > > mm/vmalloc.c | 18 +++++++++++++++++-
    > > > 2 files changed, 18 insertions(+), 1 deletion(-)
    > > >
    > > > diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
    > > > index 096d48aa3437..69250efa03d1 100644
    > > > --- a/include/linux/vmalloc.h
    > > > +++ b/include/linux/vmalloc.h
    > > > @@ -76,6 +76,7 @@ struct vmap_area {
    > > > 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 */
    > > > };
    > > >
    > > > /* archs that select HAVE_ARCH_HUGE_VMAP should override one or more of these */
    > > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
    > > > index 5d3fd3e6fe09..d6f376060d83 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);
    > > >
    > > This is not a good place to set flags to zero. It looks to me like
    > > corner and kind of specific.
    >
    > Thanks for reviewing.
    >
    > Here, I thought to clear VMAP_RAM|VMAP_BLOCK on vmap->flags when free
    > the vmap_block. I didn't find a good place to do the clearing. When we
    > call free_vmap_block(), we either come from purge_fragmented_blocks(),
    > or from vb_free(). In vb_free(), it will call free_vmap_block() when
    > the whole vmap_block is dirty. In purge_fragmented_blocks(), it will
    > try to purge all vmap_block which only has dirty or free regions.
    > For both of above functions, they will call free_vmap_block() when
    > there's no being used region in the vmap_block.
    >
    > purge_fragmented_blocks()
    > vb_free()
    > -->free_vmap_block()
    >
    > So seems we don't need to clear the VMAP_RAM|VMAP_BLOCK on vmap->flags
    > because there's no mapping existed in the vmap_block. The consequent
    > free_vmap_block() will remove the relevant vmap_area from vmap_area_list
    > and vmap_area_root tree.
    >
    > So I plan to remove code change in this place.
    > >
    > >
    > > > nr_lazy = atomic_long_add_return((va->va_end - va->va_start) >>
    > > > @@ -1887,6 +1888,10 @@ 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
    > > > +#define VMAP_FLAGS_MASK 0x3
    > > > +
    > > > struct vmap_block_queue {
    > > > spinlock_t lock;
    > > > struct list_head free;
    > > > @@ -1967,6 +1972,9 @@ 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);
    > > >
    > > The per-cpu code was created as a fast per-cpu allocator because of high
    > > vmalloc lock contention. If possible we should avoid of locking of the
    > > vmap_area_lock. Because it has a high contention.
    >
    > Fair enough. I made below draft patch to address the concern. By
    > adding argument va_flags to alloc_vmap_area(), we can pass the
    > vm_map_ram flags into alloc_vmap_area and filled into vmap_area->flags.
    > With this, we don't need add extra action to acquire vmap_area_root lock
    > and do the flags setting. Is it OK to you?
    >
    > From 115f6080b339d0cf9dd20c5f6c0d3121f6b22274 Mon Sep 17 00:00:00 2001
    > From: Baoquan He <bhe@redhat.com>
    > Date: Wed, 7 Dec 2022 11:08:14 +0800
    > Subject: [PATCH] mm/vmalloc: change alloc_vmap_area() to pass in va_flags
    >
    > With this change, we can pass and set vmap_area->flags for vm_map_ram area
    > in alloc_vmap_area(). Then no extra action need be added to acquire
    > vmap_area_lock when doing the vmap_area->flags setting.
    >
    > Signed-off-by: Baoquan He <bhe@redhat.com>
    > ---
    > mm/vmalloc.c | 13 +++++++++----
    > 1 file changed, 9 insertions(+), 4 deletions(-)
    >
    > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
    > index ccaa461998f3..d74eddec352f 100644
    > --- a/mm/vmalloc.c
    > +++ b/mm/vmalloc.c
    > @@ -1586,7 +1586,9 @@ preload_this_cpu_lock(spinlock_t *lock, gfp_t gfp_mask, int node)
    > static struct vmap_area *alloc_vmap_area(unsigned long size,
    > unsigned long align,
    > unsigned long vstart, unsigned long vend,
    > - int node, gfp_t gfp_mask)
    > + int node, gfp_t gfp_mask,
    > + unsigned long va_flags)
    > +)
    > {
    > struct vmap_area *va;
    > unsigned long freed;
    > @@ -1630,6 +1632,7 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
    > va->va_start = addr;
    > va->va_end = addr + size;
    > va->vm = NULL;
    > + va->flags = va_flags;
    >
    > spin_lock(&vmap_area_lock);
    > insert_vmap_area(va, &vmap_area_root, &vmap_area_list);
    > @@ -1961,7 +1964,8 @@ static void *new_vmap_block(unsigned int order, gfp_t gfp_mask)
    >
    > va = alloc_vmap_area(VMAP_BLOCK_SIZE, VMAP_BLOCK_SIZE,
    > VMALLOC_START, VMALLOC_END,
    > - node, gfp_mask);
    > + node, gfp_mask,
    > + VMAP_RAM|VMAP_BLOCK);
    > if (IS_ERR(va)) {
    > kfree(vb);
    > return ERR_CAST(va);
    > @@ -2258,7 +2262,8 @@ void *vm_map_ram(struct page **pages, unsigned int count, int node)
    > } else {
    > struct vmap_area *va;
    > va = alloc_vmap_area(size, PAGE_SIZE,
    > - VMALLOC_START, VMALLOC_END, node, GFP_KERNEL);
    > + VMALLOC_START, VMALLOC_END,
    > + node, GFP_KERNEL, VMAP_RAM|VMAP_BLOCK);
    > if (IS_ERR(va))
    > return NULL;
    >
    > @@ -2498,7 +2503,7 @@ static struct vm_struct *__get_vm_area_node(unsigned long size,
    > if (!(flags & VM_NO_GUARD))
    > size += PAGE_SIZE;
    >
    > - va = alloc_vmap_area(size, align, start, end, node, gfp_mask);
    > + va = alloc_vmap_area(size, align, start, end, node, gfp_mask, 0);
    > if (IS_ERR(va)) {
    > kfree(area);
    > return NULL;
    > --
    > 2.34.1
    >
    Yes, this is better than it was before. Adding an extra parameter makes
    it more valid and logical.

    --
    Uladzislau Rezki

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