MODULE_PARM_DESC(max_buffer_pages,
"Maximum number of free pages to keep in each block backend buffer");
+/*
+ * Maximum number of grants to map persistently in blkback. For maximum
+ * performance this should be the total numbers of grants that can be used
+ * to fill the ring, but since this might become too high, specially with
+ * the use of indirect descriptors, we set it to a value that provides good
+ * performance without using too much memory.
+ *
+ * When the list of persistent grants is full we clean it up using a LRU
+ * algorithm.
+ */
+
+static int xen_blkif_max_pgrants = 352;
+module_param_named(max_persistent_grants, xen_blkif_max_pgrants, int, 0644);
+MODULE_PARM_DESC(max_persistent_grants,
+ "Maximum number of grants to map persistently");
+
+/*
+ * The LRU mechanism to clean the lists of persistent grants needs to
+ * be executed periodically. The time interval between consecutive executions
+ * of the purge mechanism is set in ms.
+ */
+#define LRU_INTERVAL 100
+
+/*
+ * When the persistent grants list is full we will remove unused grants
+ * from the list. The percent number of grants to be removed at each LRU
+ * execution.
+ */
+#define LRU_PERCENT_CLEAN 5
+
/* Run-time switchable: /sys/module/blkback/parameters/ */
static unsigned int log_stats;
module_param(log_stats, int, 0644);
unsigned short operation;
int status;
struct list_head free_list;
- DECLARE_BITMAP(unmap_seg, BLKIF_MAX_SEGMENTS_PER_REQUEST);
struct page *pages[BLKIF_MAX_SEGMENTS_PER_REQUEST];
+ struct persistent_gnt *persistent_gnts[BLKIF_MAX_SEGMENTS_PER_REQUEST];
};
#define BLKBACK_INVALID_HANDLE (~0)
static struct xen_blkbk *blkbk;
-/*
- * Maximum number of grant pages that can be mapped in blkback.
- * BLKIF_MAX_SEGMENTS_PER_REQUEST * RING_SIZE is the maximum number of
- * pages that blkback will persistently map.
- * Currently, this is:
- * RING_SIZE = 32 (for all known ring types)
- * BLKIF_MAX_SEGMENTS_PER_REQUEST = 11
- * sizeof(struct persistent_gnt) = 48
- * So the maximum memory used to store the grants is:
- * 32 * 11 * 48 = 16896 bytes
- */
-static inline unsigned int max_mapped_grant_pages(enum blkif_protocol protocol)
-{
- switch (protocol) {
- case BLKIF_PROTOCOL_NATIVE:
- return __CONST_RING_SIZE(blkif, PAGE_SIZE) *
- BLKIF_MAX_SEGMENTS_PER_REQUEST;
- case BLKIF_PROTOCOL_X86_32:
- return __CONST_RING_SIZE(blkif_x86_32, PAGE_SIZE) *
- BLKIF_MAX_SEGMENTS_PER_REQUEST;
- case BLKIF_PROTOCOL_X86_64:
- return __CONST_RING_SIZE(blkif_x86_64, PAGE_SIZE) *
- BLKIF_MAX_SEGMENTS_PER_REQUEST;
- default:
- BUG();
- }
- return 0;
-}
-
-
/*
* Little helpful macro to figure out the index and virtual address of the
* pending_pages[..]. For each 'pending_req' we have have up to
(n) = (&(pos)->node != NULL) ? rb_next(&(pos)->node) : NULL)
-static int add_persistent_gnt(struct rb_root *root,
+/*
+ * We don't need locking around the persistent grant helpers
+ * because blkback uses a single-thread for each backed, so we
+ * can be sure that this functions will never be called recursively.
+ *
+ * The only exception to that is put_persistent_grant, that can be called
+ * from interrupt context (by xen_blkbk_unmap), so we have to use atomic
+ * bit operations to modify the flags of a persistent grant and to count
+ * the number of used grants.
+ */
+static int add_persistent_gnt(struct xen_blkif *blkif,
struct persistent_gnt *persistent_gnt)
{
- struct rb_node **new = &(root->rb_node), *parent = NULL;
+ struct rb_node **new = NULL, *parent = NULL;
struct persistent_gnt *this;
+ if (blkif->persistent_gnt_c >= xen_blkif_max_pgrants) {
+ if (!blkif->vbd.overflow_max_grants)
+ blkif->vbd.overflow_max_grants = 1;
+ return -EBUSY;
+ }
/* Figure out where to put new node */
+ new = &blkif->persistent_gnts.rb_node;
while (*new) {
this = container_of(*new, struct persistent_gnt, node);
}
}
+ bitmap_zero(persistent_gnt->flags, PERSISTENT_GNT_FLAGS_SIZE);
+ set_bit(PERSISTENT_GNT_ACTIVE, persistent_gnt->flags);
/* Add new node and rebalance tree. */
rb_link_node(&(persistent_gnt->node), parent, new);
- rb_insert_color(&(persistent_gnt->node), root);
+ rb_insert_color(&(persistent_gnt->node), &blkif->persistent_gnts);
+ blkif->persistent_gnt_c++;
+ atomic_inc(&blkif->persistent_gnt_in_use);
return 0;
}
-static struct persistent_gnt *get_persistent_gnt(struct rb_root *root,
+static struct persistent_gnt *get_persistent_gnt(struct xen_blkif *blkif,
grant_ref_t gref)
{
struct persistent_gnt *data;
- struct rb_node *node = root->rb_node;
+ struct rb_node *node = NULL;
+ node = blkif->persistent_gnts.rb_node;
while (node) {
data = container_of(node, struct persistent_gnt, node);
node = node->rb_left;
else if (gref > data->gnt)
node = node->rb_right;
- else
+ else {
+ if(test_bit(PERSISTENT_GNT_ACTIVE, data->flags)) {
+ pr_alert_ratelimited(DRV_PFX " requesting a grant already in use\n");
+ return NULL;
+ }
+ set_bit(PERSISTENT_GNT_ACTIVE, data->flags);
+ atomic_inc(&blkif->persistent_gnt_in_use);
return data;
+ }
}
return NULL;
}
+static void put_persistent_gnt(struct xen_blkif *blkif,
+ struct persistent_gnt *persistent_gnt)
+{
+ if(!test_bit(PERSISTENT_GNT_ACTIVE, persistent_gnt->flags))
+ pr_alert_ratelimited(DRV_PFX " freeing a grant already unused");
+ set_bit(PERSISTENT_GNT_WAS_ACTIVE, persistent_gnt->flags);
+ clear_bit(PERSISTENT_GNT_ACTIVE, persistent_gnt->flags);
+ atomic_dec(&blkif->persistent_gnt_in_use);
+}
+
static void free_persistent_gnts(struct xen_blkif *blkif, struct rb_root *root,
unsigned int num)
{
BUG_ON(num != 0);
}
+static void unmap_purged_grants(struct work_struct *work)
+{
+ struct gnttab_unmap_grant_ref unmap[BLKIF_MAX_SEGMENTS_PER_REQUEST];
+ struct page *pages[BLKIF_MAX_SEGMENTS_PER_REQUEST];
+ struct persistent_gnt *persistent_gnt;
+ int ret, segs_to_unmap = 0;
+ struct xen_blkif *blkif = container_of(work, typeof(*blkif), persistent_purge_work);
+
+ while(!list_empty(&blkif->persistent_purge_list)) {
+ persistent_gnt = list_first_entry(&blkif->persistent_purge_list,
+ struct persistent_gnt,
+ remove_node);
+ list_del(&persistent_gnt->remove_node);
+
+ gnttab_set_unmap_op(&unmap[segs_to_unmap],
+ vaddr(persistent_gnt->page),
+ GNTMAP_host_map,
+ persistent_gnt->handle);
+
+ pages[segs_to_unmap] = persistent_gnt->page;
+
+ if (++segs_to_unmap == BLKIF_MAX_SEGMENTS_PER_REQUEST) {
+ ret = gnttab_unmap_refs(unmap, NULL, pages,
+ segs_to_unmap);
+ BUG_ON(ret);
+ put_free_pages(blkif, pages, segs_to_unmap);
+ segs_to_unmap = 0;
+ }
+ kfree(persistent_gnt);
+ }
+ if (segs_to_unmap > 0) {
+ ret = gnttab_unmap_refs(unmap, NULL, pages, segs_to_unmap);
+ BUG_ON(ret);
+ put_free_pages(blkif, pages, segs_to_unmap);
+ }
+}
+
+static void purge_persistent_gnt(struct xen_blkif *blkif)
+{
+ struct persistent_gnt *persistent_gnt;
+ struct rb_node *n;
+ unsigned int num_clean, total;
+ bool scan_used = false;
+ struct rb_root *root;
+
+ if (blkif->persistent_gnt_c < xen_blkif_max_pgrants ||
+ (blkif->persistent_gnt_c == xen_blkif_max_pgrants &&
+ !blkif->vbd.overflow_max_grants)) {
+ return;
+ }
+
+ if (work_pending(&blkif->persistent_purge_work)) {
+ pr_alert_ratelimited(DRV_PFX "Scheduled work from previous purge is still pending, cannot purge list\n");
+ return;
+ }
+
+ num_clean = (xen_blkif_max_pgrants / 100) * LRU_PERCENT_CLEAN;
+ num_clean = blkif->persistent_gnt_c - xen_blkif_max_pgrants + num_clean;
+ num_clean = min(blkif->persistent_gnt_c, num_clean);
+ if (num_clean >
+ (blkif->persistent_gnt_c -
+ atomic_read(&blkif->persistent_gnt_in_use)))
+ return;
+
+ /*
+ * At this point, we can assure that there will be no calls
+ * to get_persistent_grant (because we are executing this code from
+ * xen_blkif_schedule), there can only be calls to put_persistent_gnt,
+ * which means that the number of currently used grants will go down,
+ * but never up, so we will always be able to remove the requested
+ * number of grants.
+ */
+
+ total = num_clean;
+
+ pr_debug(DRV_PFX "Going to purge %u persistent grants\n", num_clean);
+
+ INIT_LIST_HEAD(&blkif->persistent_purge_list);
+ root = &blkif->persistent_gnts;
+purge_list:
+ foreach_grant_safe(persistent_gnt, n, root, node) {
+ BUG_ON(persistent_gnt->handle ==
+ BLKBACK_INVALID_HANDLE);
+
+ if (test_bit(PERSISTENT_GNT_ACTIVE, persistent_gnt->flags))
+ continue;
+ if (!scan_used &&
+ (test_bit(PERSISTENT_GNT_WAS_ACTIVE, persistent_gnt->flags)))
+ continue;
+
+ rb_erase(&persistent_gnt->node, root);
+ list_add(&persistent_gnt->remove_node,
+ &blkif->persistent_purge_list);
+ if (--num_clean == 0)
+ goto finished;
+ }
+ /*
+ * If we get here it means we also need to start cleaning
+ * grants that were used since last purge in order to cope
+ * with the requested num
+ */
+ if (!scan_used) {
+ pr_debug(DRV_PFX "Still missing %u purged frames\n", num_clean);
+ scan_used = true;
+ goto purge_list;
+ }
+finished:
+ /* Remove the "used" flag from all the persistent grants */
+ foreach_grant_safe(persistent_gnt, n, root, node) {
+ BUG_ON(persistent_gnt->handle ==
+ BLKBACK_INVALID_HANDLE);
+ clear_bit(PERSISTENT_GNT_WAS_ACTIVE, persistent_gnt->flags);
+ }
+ blkif->persistent_gnt_c -= (total - num_clean);
+ blkif->vbd.overflow_max_grants = 0;
+
+ /* We can defer this work */
+ INIT_WORK(&blkif->persistent_purge_work, unmap_purged_grants);
+ schedule_work(&blkif->persistent_purge_work);
+ pr_debug(DRV_PFX "Purged %u/%u\n", (total - num_clean), total);
+ return;
+}
+
/*
* Retrieve from the 'pending_reqs' a free pending_req structure to be used.
*/
static void print_stats(struct xen_blkif *blkif)
{
pr_info("xen-blkback (%s): oo %3llu | rd %4llu | wr %4llu | f %4llu"
- " | ds %4llu | pg: %4u/%4u\n",
+ " | ds %4llu | pg: %4u/%4d\n",
current->comm, blkif->st_oo_req,
blkif->st_rd_req, blkif->st_wr_req,
blkif->st_f_req, blkif->st_ds_req,
blkif->persistent_gnt_c,
- max_mapped_grant_pages(blkif->blk_protocol));
+ xen_blkif_max_pgrants);
blkif->st_print = jiffies + msecs_to_jiffies(10 * 1000);
blkif->st_rd_req = 0;
blkif->st_wr_req = 0;
{
struct xen_blkif *blkif = arg;
struct xen_vbd *vbd = &blkif->vbd;
+ unsigned long timeout;
xen_blkif_get(blkif);
if (unlikely(vbd->size != vbd_sz(vbd)))
xen_vbd_resize(blkif);
- wait_event_interruptible(
+ timeout = msecs_to_jiffies(LRU_INTERVAL);
+
+ timeout = wait_event_interruptible_timeout(
blkif->wq,
- blkif->waiting_reqs || kthread_should_stop());
- wait_event_interruptible(
+ blkif->waiting_reqs || kthread_should_stop(),
+ timeout);
+ if (timeout == 0)
+ goto purge_gnt_list;
+ timeout = wait_event_interruptible_timeout(
blkbk->pending_free_wq,
!list_empty(&blkbk->pending_free) ||
- kthread_should_stop());
+ kthread_should_stop(),
+ timeout);
+ if (timeout == 0)
+ goto purge_gnt_list;
blkif->waiting_reqs = 0;
smp_mb(); /* clear flag *before* checking for work */
if (do_block_io_op(blkif))
blkif->waiting_reqs = 1;
+purge_gnt_list:
+ if (blkif->vbd.feature_gnt_persistent &&
+ time_after(jiffies, blkif->next_lru)) {
+ purge_persistent_gnt(blkif);
+ blkif->next_lru = jiffies + msecs_to_jiffies(LRU_INTERVAL);
+ }
+
/* Shrink if we have more than xen_blkif_max_buffer_pages */
shrink_free_pagepool(blkif, xen_blkif_max_buffer_pages);
int ret;
for (i = 0; i < req->nr_pages; i++) {
- if (!test_bit(i, req->unmap_seg))
+ if (req->persistent_gnts[i] != NULL) {
+ put_persistent_gnt(blkif, req->persistent_gnts[i]);
continue;
+ }
handle = pending_handle(req, i);
pages[invcount] = req->pages[i];
if (handle == BLKBACK_INVALID_HANDLE)
struct page *pages[])
{
struct gnttab_map_grant_ref map[BLKIF_MAX_SEGMENTS_PER_REQUEST];
- struct persistent_gnt *persistent_gnts[BLKIF_MAX_SEGMENTS_PER_REQUEST];
struct page *pages_to_gnt[BLKIF_MAX_SEGMENTS_PER_REQUEST];
+ struct persistent_gnt **persistent_gnts = pending_req->persistent_gnts;
struct persistent_gnt *persistent_gnt = NULL;
struct xen_blkif *blkif = pending_req->blkif;
phys_addr_t addr = 0;
use_persistent_gnts = (blkif->vbd.feature_gnt_persistent);
- BUG_ON(blkif->persistent_gnt_c >
- max_mapped_grant_pages(pending_req->blkif->blk_protocol));
-
/*
* Fill out preq.nr_sects with proper amount of sectors, and setup
* assign map[..] with the PFN of the page in our domain with the
if (use_persistent_gnts)
persistent_gnt = get_persistent_gnt(
- &blkif->persistent_gnts,
+ blkif,
req->u.rw.seg[i].gref);
if (persistent_gnt) {
* so that when we access vaddr(pending_req,i) it has the contents of
* the page from the other domain.
*/
- bitmap_zero(pending_req->unmap_seg, BLKIF_MAX_SEGMENTS_PER_REQUEST);
for (seg_idx = 0, new_map_idx = 0; seg_idx < nseg; seg_idx++) {
if (!persistent_gnts[seg_idx]) {
/* This is a newly mapped grant */
goto next;
}
if (use_persistent_gnts &&
- blkif->persistent_gnt_c <
- max_mapped_grant_pages(blkif->blk_protocol)) {
+ blkif->persistent_gnt_c < xen_blkif_max_pgrants) {
/*
* We are using persistent grants, the grant is
- * not mapped but we have room for it
+ * not mapped but we might have room for it.
*/
persistent_gnt = kmalloc(sizeof(struct persistent_gnt),
GFP_KERNEL);
persistent_gnt->gnt = map[new_map_idx].ref;
persistent_gnt->handle = map[new_map_idx].handle;
persistent_gnt->page = pages[seg_idx];
- if (add_persistent_gnt(&blkif->persistent_gnts,
+ if (add_persistent_gnt(blkif,
persistent_gnt)) {
kfree(persistent_gnt);
persistent_gnt = NULL;
goto next_unmap;
}
- blkif->persistent_gnt_c++;
+ persistent_gnts[seg_idx] = persistent_gnt;
pr_debug(DRV_PFX " grant %u added to the tree of persistent grants, using %u/%u\n",
persistent_gnt->gnt, blkif->persistent_gnt_c,
- max_mapped_grant_pages(blkif->blk_protocol));
+ xen_blkif_max_pgrants);
new_map_idx++;
goto next;
}
* We could not map this grant persistently, so use it as
* a non-persistent grant.
*/
- bitmap_set(pending_req->unmap_seg, seg_idx, 1);
new_map_idx++;
next:
seg[seg_idx].offset = (req->u.rw.seg[seg_idx].first_sect << 9);
projects / linux-beck.git / commitdiff