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mm/hugetlb_vmemmap: batch HVO work when demoting

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Batch the HVO work, including de-HVO of the source and HVO of the
destination hugeTLB folios, to speed up demotion.

After commit bd225530a4 ("mm/hugetlb_vmemmap: fix race with speculative
PFN walkers"), each request of HVO or de-HVO, batched or not, invokes
synchronize_rcu() once.  For example, when not batched, demoting one 1GB
hugeTLB folio to 512 2MB hugeTLB folios invokes synchronize_rcu() 513
times (1 de-HVO plus 512 HVO requests), whereas when batched, only twice
(1 de-HVO plus 1 HVO request).  And the performance difference between the
two cases is significant, e.g.,

  echo 2048kB >/sys/kernel/mm/hugepages/hugepages-1048576kB/demote_size
  time echo 100 >/sys/kernel/mm/hugepages/hugepages-1048576kB/demote

Before this patch:
  real     8m58.158s
  user     0m0.009s
  sys      0m5.900s

After this patch:
  real     0m0.900s
  user     0m0.000s
  sys      0m0.851s

Note that this patch changes the behavior of the `demote` interface when
de-HVO fails.  Before, the interface aborts immediately upon failure; now,
it tries to finish an entire batch, meaning it can make extra progress if
the rest of the batch contains folios that do not need to de-HVO.

Link: https://lkml.kernel.org/r/20240812224823.3914837-1-yuzhao@google.com
Fixes: bd225530a4 ("mm/hugetlb_vmemmap: fix race with speculative PFN walkers")
Signed-off-by: Yu Zhao <yuzhao@google.com>
Reviewed-by: Muchun Song <muchun.song@linux.dev>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Yu Zhao 2024-08-12 16:48:23 -06:00 committed by Andrew Morton
parent 67b9a353e1
commit c0f398c3b2
1 changed files with 107 additions and 79 deletions
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186
mm/hugetlb.c
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@ -3921,100 +3921,124 @@ out:
return 0;
}
static int demote_free_hugetlb_folio(struct hstate *h, struct folio *folio)
static long demote_free_hugetlb_folios(struct hstate *src, struct hstate *dst,
struct list_head *src_list)
{
int i, nid = folio_nid(folio);
struct hstate *target_hstate;
struct page *subpage;
struct folio *inner_folio;
int rc = 0;
long rc;
struct folio *folio, *next;
LIST_HEAD(dst_list);
LIST_HEAD(ret_list);
target_hstate = size_to_hstate(PAGE_SIZE << h->demote_order);
remove_hugetlb_folio(h, folio, false);
spin_unlock_irq(&hugetlb_lock);
/*
* If vmemmap already existed for folio, the remove routine above would
* have cleared the hugetlb folio flag. Hence the folio is technically
* no longer a hugetlb folio. hugetlb_vmemmap_restore_folio can only be
* passed hugetlb folios and will BUG otherwise.
*/
if (folio_test_hugetlb(folio)) {
rc = hugetlb_vmemmap_restore_folio(h, folio);
if (rc) {
/* Allocation of vmemmmap failed, we can not demote folio */
spin_lock_irq(&hugetlb_lock);
add_hugetlb_folio(h, folio, false);
return rc;
}
}
/*
* Use destroy_compound_hugetlb_folio_for_demote for all huge page
* sizes as it will not ref count folios.
*/
destroy_compound_hugetlb_folio_for_demote(folio, huge_page_order(h));
rc = hugetlb_vmemmap_restore_folios(src, src_list, &ret_list);
list_splice_init(&ret_list, src_list);
/*
* Taking target hstate mutex synchronizes with set_max_huge_pages.
* Without the mutex, pages added to target hstate could be marked
* as surplus.
*
* Note that we already hold h->resize_lock. To prevent deadlock,
* Note that we already hold src->resize_lock. To prevent deadlock,
* use the convention of always taking larger size hstate mutex first.
*/
mutex_lock(&target_hstate->resize_lock);
for (i = 0; i < pages_per_huge_page(h);
i += pages_per_huge_page(target_hstate)) {
subpage = folio_page(folio, i);
inner_folio = page_folio(subpage);
if (hstate_is_gigantic(target_hstate))
prep_compound_gigantic_folio_for_demote(inner_folio,
target_hstate->order);
else
prep_compound_page(subpage, target_hstate->order);
folio_change_private(inner_folio, NULL);
prep_new_hugetlb_folio(target_hstate, inner_folio, nid);
free_huge_folio(inner_folio);
}
mutex_unlock(&target_hstate->resize_lock);
mutex_lock(&dst->resize_lock);
spin_lock_irq(&hugetlb_lock);
list_for_each_entry_safe(folio, next, src_list, lru) {
int i;
if (folio_test_hugetlb_vmemmap_optimized(folio))
continue;
list_del(&folio->lru);
/*
* Use destroy_compound_hugetlb_folio_for_demote for all huge page
* sizes as it will not ref count folios.
*/
destroy_compound_hugetlb_folio_for_demote(folio, huge_page_order(src));
for (i = 0; i < pages_per_huge_page(src); i += pages_per_huge_page(dst)) {
struct page *page = folio_page(folio, i);
if (hstate_is_gigantic(dst))
prep_compound_gigantic_folio_for_demote(page_folio(page),
dst->order);
else
prep_compound_page(page, dst->order);
set_page_private(page, 0);
init_new_hugetlb_folio(dst, page_folio(page));
list_add(&page->lru, &dst_list);
}
}
prep_and_add_allocated_folios(dst, &dst_list);
mutex_unlock(&dst->resize_lock);
return rc;
}
static long demote_pool_huge_page(struct hstate *src, nodemask_t *nodes_allowed,
unsigned long nr_to_demote)
__must_hold(&hugetlb_lock)
{
int nr_nodes, node;
struct hstate *dst;
long rc = 0;
long nr_demoted = 0;
lockdep_assert_held(&hugetlb_lock);
/* We should never get here if no demote order */
if (!src->demote_order) {
pr_warn("HugeTLB: NULL demote order passed to demote_pool_huge_page.\n");
return -EINVAL; /* internal error */
}
dst = size_to_hstate(PAGE_SIZE << src->demote_order);
for_each_node_mask_to_free(src, nr_nodes, node, nodes_allowed) {
LIST_HEAD(list);
struct folio *folio, *next;
list_for_each_entry_safe(folio, next, &src->hugepage_freelists[node], lru) {
if (folio_test_hwpoison(folio))
continue;
remove_hugetlb_folio(src, folio, false);
list_add(&folio->lru, &list);
if (++nr_demoted == nr_to_demote)
break;
}
spin_unlock_irq(&hugetlb_lock);
rc = demote_free_hugetlb_folios(src, dst, &list);
spin_lock_irq(&hugetlb_lock);
list_for_each_entry_safe(folio, next, &list, lru) {
list_del(&folio->lru);
add_hugetlb_folio(src, folio, false);
nr_demoted--;
}
if (rc < 0 || nr_demoted == nr_to_demote)
break;
}
/*
* Not absolutely necessary, but for consistency update max_huge_pages
* based on pool changes for the demoted page.
*/
h->max_huge_pages--;
target_hstate->max_huge_pages +=
pages_per_huge_page(h) / pages_per_huge_page(target_hstate);
src->max_huge_pages -= nr_demoted;
dst->max_huge_pages += nr_demoted << (huge_page_order(src) - huge_page_order(dst));
return rc;
}
static int demote_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed)
__must_hold(&hugetlb_lock)
{
int nr_nodes, node;
struct folio *folio;
lockdep_assert_held(&hugetlb_lock);
/* We should never get here if no demote order */
if (!h->demote_order) {
pr_warn("HugeTLB: NULL demote order passed to demote_pool_huge_page.\n");
return -EINVAL; /* internal error */
}
for_each_node_mask_to_free(h, nr_nodes, node, nodes_allowed) {
list_for_each_entry(folio, &h->hugepage_freelists[node], lru) {
if (folio_test_hwpoison(folio))
continue;
return demote_free_hugetlb_folio(h, folio);
}
}
if (rc < 0)
return rc;
if (nr_demoted)
return nr_demoted;
/*
* Only way to get here is if all pages on free lists are poisoned.
* Return -EBUSY so that caller will not retry.
@ -4249,6 +4273,8 @@ static ssize_t demote_store(struct kobject *kobj,
spin_lock_irq(&hugetlb_lock);
while (nr_demote) {
long rc;
/*
* Check for available pages to demote each time thorough the
* loop as demote_pool_huge_page will drop hugetlb_lock.
@ -4261,11 +4287,13 @@ static ssize_t demote_store(struct kobject *kobj,
if (!nr_available)
break;
err = demote_pool_huge_page(h, n_mask);
if (err)
rc = demote_pool_huge_page(h, n_mask, nr_demote);
if (rc < 0) {
err = rc;
break;
}
nr_demote--;
nr_demote -= rc;
}
spin_unlock_irq(&hugetlb_lock);