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mm: vmalloc: improve description of vmap node layer

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This patch adds extra explanation of recently added vmap node layer based
on community feedback.  No functional change.

Link: https://lkml.kernel.org/r/20240124180920.50725-1-urezki@gmail.com
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Oleksiy Avramchenko <oleksiy.avramchenko@sony.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Uladzislau Rezki (Sony) 2024-01-24 19:09:19 +01:00 committed by Andrew Morton
parent 7679ba6b36
commit 15e02a39fb
1 changed files with 46 additions and 14 deletions
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60
mm/vmalloc.c
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@ -765,9 +765,10 @@ static struct rb_root free_vmap_area_root = RB_ROOT;
static DEFINE_PER_CPU(struct vmap_area *, ne_fit_preload_node);
/*
* An effective vmap-node logic. Users make use of nodes instead
* of a global heap. It allows to balance an access and mitigate
* contention.
* This structure defines a single, solid model where a list and
* rb-tree are part of one entity protected by the lock. Nodes are
* sorted in ascending order, thus for O(1) access to left/right
* neighbors a list is used as well as for sequential traversal.
*/
struct rb_list {
struct rb_root root;
@ -775,16 +776,23 @@ struct rb_list {
spinlock_t lock;
};
/*
* A fast size storage contains VAs up to 1M size. A pool consists
* of linked between each other ready to go VAs of certain sizes.
* An index in the pool-array corresponds to number of pages + 1.
*/
#define MAX_VA_SIZE_PAGES 256
struct vmap_pool {
struct list_head head;
unsigned long len;
};
/*
* A fast size storage contains VAs up to 1M size.
* An effective vmap-node logic. Users make use of nodes instead
* of a global heap. It allows to balance an access and mitigate
* contention.
*/
#define MAX_VA_SIZE_PAGES 256
static struct vmap_node {
/* Simple size segregated storage. */
struct vmap_pool pool[MAX_VA_SIZE_PAGES];
@ -803,6 +811,11 @@ static struct vmap_node {
unsigned long nr_purged;
} single;
/*
* Initial setup consists of one single node, i.e. a balancing
* is fully disabled. Later on, after vmap is initialized these
* parameters are updated based on a system capacity.
*/
static struct vmap_node *vmap_nodes = &single;
static __read_mostly unsigned int nr_vmap_nodes = 1;
static __read_mostly unsigned int vmap_zone_size = 1;
@ -2048,7 +2061,12 @@ decay_va_pool_node(struct vmap_node *vn, bool full_decay)
}
}
/* Attach the pool back if it has been partly decayed. */
/*
* Attach the pool back if it has been partly decayed.
* Please note, it is supposed that nobody(other contexts)
* can populate the pool therefore a simple list replace
* operation takes place here.
*/
if (!full_decay && !list_empty(&tmp_list)) {
spin_lock(&vn->pool_lock);
list_replace_init(&tmp_list, &vn->pool[i].head);
@ -2257,16 +2275,14 @@ struct vmap_area *find_vmap_area(unsigned long addr)
* An addr_to_node_id(addr) converts an address to a node index
* where a VA is located. If VA spans several zones and passed
* addr is not the same as va->va_start, what is not common, we
* may need to scan an extra nodes. See an example:
* may need to scan extra nodes. See an example:
*
* <--va-->
* <----va---->
* -|-----|-----|-----|-----|-
* 1 2 0 1
*
* VA resides in node 1 whereas it spans 1 and 2. If passed
* addr is within a second node we should do extra work. We
* should mention that it is rare and is a corner case from
* the other hand it has to be covered.
* VA resides in node 1 whereas it spans 1, 2 an 0. If passed
* addr is within 2 or 0 nodes we should do extra work.
*/
i = j = addr_to_node_id(addr);
do {
@ -2289,6 +2305,9 @@ static struct vmap_area *find_unlink_vmap_area(unsigned long addr)
struct vmap_area *va;
int i, j;
/*
* Check the comment in the find_vmap_area() about the loop.
*/
i = j = addr_to_node_id(addr);
do {
vn = &vmap_nodes[i];
@ -4882,7 +4901,20 @@ static void vmap_init_nodes(void)
int i, n;
#if BITS_PER_LONG == 64
/* A high threshold of max nodes is fixed and bound to 128. */
/*
* A high threshold of max nodes is fixed and bound to 128,
* thus a scale factor is 1 for systems where number of cores
* are less or equal to specified threshold.
*
* As for NUMA-aware notes. For bigger systems, for example
* NUMA with multi-sockets, where we can end-up with thousands
* of cores in total, a "sub-numa-clustering" should be added.
*
* In this case a NUMA domain is considered as a single entity
* with dedicated sub-nodes in it which describe one group or
* set of cores. Therefore a per-domain purging is supposed to
* be added as well as a per-domain balancing.
*/
n = clamp_t(unsigned int, num_possible_cpus(), 1, 128);
if (n > 1) {