The patch titled
Subject: mm/hugetlb_vmemmap: batch HVO work when demoting
has been added to the -mm mm-unstable branch. Its filename is
mm-hugetlb_vmemmap-batch-hvo-work-when-demoting.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-hugetlb_vmemmap-batch-hvo-work-when-demoting.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Yu Zhao <yuzhao@xxxxxxxxxx>
Subject: mm/hugetlb_vmemmap: batch HVO work when demoting
Date: Mon, 12 Aug 2024 16:48:23 -0600
Batch the HVO work, including de-HVO of the source and HVO of the
destination hugeTLB folios, to speed up demotion.
After commit bd225530a4c7 ("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@xxxxxxxxxx
Fixes: bd225530a4c7 ("mm/hugetlb_vmemmap: fix race with speculative PFN walkers")
Signed-off-by: Yu Zhao <yuzhao@xxxxxxxxxx>
Reviewed-by: Muchun Song <muchun.song@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/hugetlb.c | 156 ++++++++++++++++++++++++++++---------------------
1 file changed, 92 insertions(+), 64 deletions(-)
--- a/mm/hugetlb.c~mm-hugetlb_vmemmap-batch-hvo-work-when-demoting
+++ a/mm/hugetlb.c
@@ -3922,101 +3922,125 @@ 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_lock(&dst->resize_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);
+ }
}
- mutex_unlock(&target_hstate->resize_lock);
- spin_lock_irq(&hugetlb_lock);
+ prep_and_add_allocated_folios(dst, &dst_list);
- /*
- * 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);
+ mutex_unlock(&dst->resize_lock);
return rc;
}
-static int demote_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed)
+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 folio *folio;
+ 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 (!h->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(h, nr_nodes, node, nodes_allowed) {
- list_for_each_entry(folio, &h->hugepage_freelists[node], lru) {
+ 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;
- return demote_free_hugetlb_folio(h, folio);
+
+ 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.
+ */
+ src->max_huge_pages -= nr_demoted;
+ dst->max_huge_pages += nr_demoted << (huge_page_order(src) - huge_page_order(dst));
+
+ 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.
*/
@@ -4250,6 +4274,8 @@ static ssize_t demote_store(struct kobje
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.
@@ -4262,11 +4288,13 @@ static ssize_t demote_store(struct kobje
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);
_
Patches currently in -mm which might be from yuzhao@xxxxxxxxxx are
mm-hugetlb_vmemmap-dont-synchronize_rcu-without-hvo.patch
mm-swap-reduce-indentation-level.patch
mm-swap-rename-cpu_fbatches-activate.patch
mm-swap-fold-lru_rotate-into-cpu_fbatches.patch
mm-swap-remove-remaining-_fn-suffix.patch
mm-swap-remove-boilerplate.patch
mm-swap-remove-boilerplate-fix.patch
mm-free-zapped-tail-pages-when-splitting-isolated-thp.patch
mm-remap-unused-subpages-to-shared-zeropage-when-splitting-isolated-thp.patch
mm-hugetlb_vmemmap-batch-hvo-work-when-demoting.patch
