From nobody Wed Feb 11 05:04:54 2026 Received: from out30-97.freemail.mail.aliyun.com (out30-97.freemail.mail.aliyun.com [115.124.30.97]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 827FE1420D0 for ; Tue, 27 Feb 2024 13:52:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.97 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1709041963; cv=none; b=p9OIJw3xraorhXQmFSkE9/UzWeaNNpBWmgcdmJompjweyI668Tfkg5AHWdoYljzxzeDGBrnnXelQV4FhzwErV0C0uGdFlfgMlg+P6n2+ZhNdpq2VRqZVMth9HZNPVorQwSIbOdvOGxjuskNLZsy+0gfv/IRd197YCboWtmFov3I= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1709041963; c=relaxed/simple; bh=X8NNHUf6EO6XtKsBok97wPMwUXPF3HgsaY7PdvrfU7M=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=Pz2tSSeKDIF9p3cimxTUVKntv5EEPhI/9yAwdr6W5uxXYp07nOo4vm1o5rqYR4WfstKvUFceYzyksRUJG+6AK1GNGZU44tNlNNgP7vnTxutat9LX7H54LGsCM2/sXYg3hfIym/QWCnJT3glbP4IH/y/qjHkIq8V6y/nIBBVoGtw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=V49jqNvO; arc=none smtp.client-ip=115.124.30.97 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="V49jqNvO" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1709041956; h=From:To:Subject:Date:Message-Id:MIME-Version; bh=vclFUdHEbEOLvLac5txTbNN5X/YAQNb/V/s0HCQPExw=; b=V49jqNvOGlo/kH+WCaweqCN76eS71atV/3oCuHt9MQcG+WKIDJN6PQigadLFgYQx4g8q3FK0gKYennx9aVKT9WSCVW3NEQ4eVKBDLX5YAIqd4udQzAxX2CKyXNpOOHpXbDxPWGdhk4qP18vkjMzZl28xGge2bkrR4Zx56TBZEX8= X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R111e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018045192;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=10;SR=0;TI=SMTPD_---0W1N-REC_1709041955; Received: from localhost(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0W1N-REC_1709041955) by smtp.aliyun-inc.com; Tue, 27 Feb 2024 21:52:35 +0800 From: Baolin Wang To: akpm@linux-foundation.org Cc: muchun.song@linux.dev, osalvador@suse.de, david@redhat.com, linmiaohe@huawei.com, naoya.horiguchi@nec.com, mhocko@kernel.org, baolin.wang@linux.alibaba.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH 1/3] mm: record the migration reason for struct migration_target_control Date: Tue, 27 Feb 2024 21:52:25 +0800 Message-Id: X-Mailer: git-send-email 2.39.3 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" To support different hugetlb allocation strategies during hugetlb migration based on various migration reasons, recording the migration reason for the migration_target_control structure as a preparation. Signed-off-by: Baolin Wang Reviewed-by: Oscar Salvador --- mm/gup.c | 1 + mm/internal.h | 1 + mm/memory-failure.c | 1 + mm/memory_hotplug.c | 1 + mm/mempolicy.c | 1 + mm/migrate.c | 1 + mm/page_alloc.c | 1 + mm/vmscan.c | 3 ++- 8 files changed, 9 insertions(+), 1 deletion(-) diff --git a/mm/gup.c b/mm/gup.c index df83182ec72d..959a1a05b059 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -2132,6 +2132,7 @@ static int migrate_longterm_unpinnable_pages( struct migration_target_control mtc =3D { .nid =3D NUMA_NO_NODE, .gfp_mask =3D GFP_USER | __GFP_NOWARN, + .reason =3D MR_LONGTERM_PIN, }; =20 if (migrate_pages(movable_page_list, alloc_migration_target, diff --git a/mm/internal.h b/mm/internal.h index 2b7efffbe4d7..47edf69b6ee6 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -959,6 +959,7 @@ struct migration_target_control { int nid; /* preferred node id */ nodemask_t *nmask; gfp_t gfp_mask; + enum migrate_reason reason; }; =20 /* diff --git a/mm/memory-failure.c b/mm/memory-failure.c index 9349948f1abf..780bb2aee0af 100644 --- a/mm/memory-failure.c +++ b/mm/memory-failure.c @@ -2666,6 +2666,7 @@ static int soft_offline_in_use_page(struct page *page) struct migration_target_control mtc =3D { .nid =3D NUMA_NO_NODE, .gfp_mask =3D GFP_USER | __GFP_MOVABLE | __GFP_RETRY_MAYFAIL, + .reason =3D MR_MEMORY_FAILURE, }; =20 if (!huge && folio_test_large(folio)) { diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index a444e2d7dd2b..b79ba36e09e0 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -1841,6 +1841,7 @@ static void do_migrate_range(unsigned long start_pfn,= unsigned long end_pfn) struct migration_target_control mtc =3D { .nmask =3D &nmask, .gfp_mask =3D GFP_USER | __GFP_MOVABLE | __GFP_RETRY_MAYFAIL, + .reason =3D MR_MEMORY_HOTPLUG, }; int ret; =20 diff --git a/mm/mempolicy.c b/mm/mempolicy.c index f60b4c99f130..98ceb12e0e17 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -1070,6 +1070,7 @@ static long migrate_to_node(struct mm_struct *mm, int= source, int dest, struct migration_target_control mtc =3D { .nid =3D dest, .gfp_mask =3D GFP_HIGHUSER_MOVABLE | __GFP_THISNODE, + .reason =3D MR_SYSCALL, }; =20 nodes_clear(nmask); diff --git a/mm/migrate.c b/mm/migrate.c index 73a052a382f1..bde63010a3cf 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -2060,6 +2060,7 @@ static int do_move_pages_to_node(struct list_head *pa= gelist, int node) struct migration_target_control mtc =3D { .nid =3D node, .gfp_mask =3D GFP_HIGHUSER_MOVABLE | __GFP_THISNODE, + .reason =3D MR_SYSCALL, }; =20 err =3D migrate_pages(pagelist, alloc_migration_target, NULL, diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 96839b210abe..8e6dd3a1028b 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -6266,6 +6266,7 @@ int __alloc_contig_migrate_range(struct compact_contr= ol *cc, struct migration_target_control mtc =3D { .nid =3D zone_to_nid(cc->zone), .gfp_mask =3D GFP_USER | __GFP_MOVABLE | __GFP_RETRY_MAYFAIL, + .reason =3D MR_CONTIG_RANGE, }; =20 lru_cache_disable(); diff --git a/mm/vmscan.c b/mm/vmscan.c index 402c290fbf5a..510f438bb9e0 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -978,7 +978,8 @@ static unsigned int demote_folio_list(struct list_head = *demote_folios, .gfp_mask =3D (GFP_HIGHUSER_MOVABLE & ~__GFP_RECLAIM) | __GFP_NOWARN | __GFP_NOMEMALLOC | GFP_NOWAIT, .nid =3D target_nid, - .nmask =3D &allowed_mask + .nmask =3D &allowed_mask, + .reason =3D MR_DEMOTION, }; =20 if (list_empty(demote_folios)) --=20 2.39.3 From nobody Wed Feb 11 05:04:54 2026 Received: from out30-113.freemail.mail.aliyun.com (out30-113.freemail.mail.aliyun.com [115.124.30.113]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A6178145FE2 for ; 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Tue, 27 Feb 2024 21:52:36 +0800 From: Baolin Wang To: akpm@linux-foundation.org Cc: muchun.song@linux.dev, osalvador@suse.de, david@redhat.com, linmiaohe@huawei.com, naoya.horiguchi@nec.com, mhocko@kernel.org, baolin.wang@linux.alibaba.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH 2/3] mm: hugetlb: make the hugetlb migration strategy consistent Date: Tue, 27 Feb 2024 21:52:26 +0800 Message-Id: X-Mailer: git-send-email 2.39.3 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" As discussed in previous thread [1], there is an inconsistency when handing hugetlb migration. When handling the migration of freed hugetlb, it prevents fallback to other NUMA nodes in alloc_and_dissolve_hugetlb_folio(). However, when dealing with in-use hugetlb, it allows fallback to other NUMA nodes in alloc_hugetlb_folio_nodemask(), which can break the per-node hugetlb pool and might result in unexpected failures when node bound workloads doesn't g= et what is asssumed available. To make hugetlb migration strategy more clear, we should list all the scena= rios of hugetlb migration and analyze whether allocation fallback is permitted: 1) Memory offline: will call dissolve_free_huge_pages() to free the freed h= ugetlb, and call do_migrate_range() to migrate the in-use hugetlb. Both can break t= he per-node hugetlb pool, but as this is an explicit offlining operation, no b= etter choice. So should allow the hugetlb allocation fallback. 2) Memory failure: same as memory offline. Should allow fallback to a diffe= rent node might be the only option to handle it, otherwise the impact of poisoned mem= ory can be amplified. 3) Longterm pinning: will call migrate_longterm_unpinnable_pages() to migra= te in-use and not-longterm-pinnable hugetlb, which can break the per-node pool. But w= e should fail to longterm pinning if can not allocate on current node to avoid break= ing the per-node pool. 4) Syscalls (mbind, migrate_pages, move_pages): these are explicit users op= eration to move pages to other nodes, so fallback to other nodes should not be proh= ibited. 5) alloc_contig_range: used by CMA allocation and virtio-mem fake-offline t= o allocate given range of pages. Now the freed hugetlb migration is not allowed to fal= lback, to keep consistency, the in-use hugetlb migration should be also not allowed t= o fallback. 6) alloc_contig_pages: used by kfence, pgtable_debug etc. The strategy shou= ld be consistent with that of alloc_contig_range(). Based on the analysis of the various scenarios above, determine whether fal= lback is permitted according to the migration reason in alloc_migrate_hugetlb_folio(= ). [1] https://lore.kernel.org/all/6f26ce22d2fcd523418a085f2c588fe0776d46e7.17= 06794035.git.baolin.wang@linux.alibaba.com/ Signed-off-by: Baolin Wang --- include/linux/hugetlb.h | 4 ++-- mm/hugetlb.c | 39 +++++++++++++++++++++++++++++++++++---- mm/mempolicy.c | 2 +- mm/migrate.c | 2 +- 4 files changed, 39 insertions(+), 8 deletions(-) diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index 77b30a8c6076..fa122dc509cf 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -747,7 +747,7 @@ int isolate_or_dissolve_huge_page(struct page *page, st= ruct list_head *list); struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma, unsigned long addr, int avoid_reserve); struct folio *alloc_hugetlb_folio_nodemask(struct hstate *h, int preferred= _nid, - nodemask_t *nmask, gfp_t gfp_mask); + nodemask_t *nmask, gfp_t gfp_mask, int reason); int hugetlb_add_to_page_cache(struct folio *folio, struct address_space *m= apping, pgoff_t idx); void restore_reserve_on_error(struct hstate *h, struct vm_area_struct *vma, @@ -1065,7 +1065,7 @@ static inline struct folio *alloc_hugetlb_folio(struc= t vm_area_struct *vma, =20 static inline struct folio * alloc_hugetlb_folio_nodemask(struct hstate *h, int preferred_nid, - nodemask_t *nmask, gfp_t gfp_mask) + nodemask_t *nmask, gfp_t gfp_mask, int reason) { return NULL; } diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 418d66953224..e8eb08bbc688 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -2567,13 +2567,38 @@ static struct folio *alloc_surplus_hugetlb_folio(st= ruct hstate *h, } =20 static struct folio *alloc_migrate_hugetlb_folio(struct hstate *h, gfp_t g= fp_mask, - int nid, nodemask_t *nmask) + int nid, nodemask_t *nmask, int reason) { struct folio *folio; + bool allowed_fallback =3D false; =20 if (hstate_is_gigantic(h)) return NULL; =20 + if (gfp_mask & __GFP_THISNODE) + goto alloc_new; + + /* + * Note: the memory offline, memory failure and migration syscalls will + * be allowed to fallback to other nodes due to lack of a better chioce, + * that might break the per-node hugetlb pool. While other cases will + * set the __GFP_THISNODE to avoid breaking the per-node hugetlb pool. + */ + switch (reason) { + case MR_MEMORY_HOTPLUG: + case MR_MEMORY_FAILURE: + case MR_SYSCALL: + case MR_MEMPOLICY_MBIND: + allowed_fallback =3D true; + break; + default: + break; + } + + if (!allowed_fallback) + gfp_mask |=3D __GFP_THISNODE; + +alloc_new: folio =3D alloc_fresh_hugetlb_folio(h, gfp_mask, nid, nmask, NULL); if (!folio) return NULL; @@ -2621,7 +2646,7 @@ struct folio *alloc_buddy_hugetlb_folio_with_mpol(str= uct hstate *h, =20 /* folio migration callback function */ struct folio *alloc_hugetlb_folio_nodemask(struct hstate *h, int preferred= _nid, - nodemask_t *nmask, gfp_t gfp_mask) + nodemask_t *nmask, gfp_t gfp_mask, int reason) { spin_lock_irq(&hugetlb_lock); if (available_huge_pages(h)) { @@ -2636,7 +2661,7 @@ struct folio *alloc_hugetlb_folio_nodemask(struct hst= ate *h, int preferred_nid, } spin_unlock_irq(&hugetlb_lock); =20 - return alloc_migrate_hugetlb_folio(h, gfp_mask, preferred_nid, nmask); + return alloc_migrate_hugetlb_folio(h, gfp_mask, preferred_nid, nmask, rea= son); } =20 /* @@ -6653,7 +6678,13 @@ static struct folio *alloc_hugetlb_folio_vma(struct = hstate *h, =20 gfp_mask =3D htlb_alloc_mask(h); node =3D huge_node(vma, address, gfp_mask, &mpol, &nodemask); - folio =3D alloc_hugetlb_folio_nodemask(h, node, nodemask, gfp_mask); + /* + * This is used to allocate a temporary hugetlb to hold the copied + * content, which will then be copied again to the final hugetlb + * consuming a reservation. Set the migrate reason to -1 to indicate + * that breaking the per-node hugetlb pool is not allowed in this case. + */ + folio =3D alloc_hugetlb_folio_nodemask(h, node, nodemask, gfp_mask, -1); mpol_cond_put(mpol); =20 return folio; diff --git a/mm/mempolicy.c b/mm/mempolicy.c index 98ceb12e0e17..436e817eeaeb 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -1228,7 +1228,7 @@ static struct folio *alloc_migration_target_by_mpol(s= truct folio *src, h =3D folio_hstate(src); gfp =3D htlb_alloc_mask(h); nodemask =3D policy_nodemask(gfp, pol, ilx, &nid); - return alloc_hugetlb_folio_nodemask(h, nid, nodemask, gfp); + return alloc_hugetlb_folio_nodemask(h, nid, nodemask, gfp, MR_MEMPOLICY_= MBIND); } =20 if (folio_test_large(src)) diff --git a/mm/migrate.c b/mm/migrate.c index bde63010a3cf..0c2b70800da3 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -2022,7 +2022,7 @@ struct folio *alloc_migration_target(struct folio *sr= c, unsigned long private) =20 gfp_mask =3D htlb_modify_alloc_mask(h, gfp_mask); return alloc_hugetlb_folio_nodemask(h, nid, - mtc->nmask, gfp_mask); + mtc->nmask, gfp_mask, mtc->reason); } =20 if (folio_test_large(src)) { --=20 2.39.3 From nobody Wed Feb 11 05:04:55 2026 Received: from out30-133.freemail.mail.aliyun.com (out30-133.freemail.mail.aliyun.com [115.124.30.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 862601420A6 for ; Tue, 27 Feb 2024 13:52:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.133 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1709041962; cv=none; b=DROcn0oUVdUzm0cIhDYShct/P36vURNviLqtPqTM7GX8Rq48sfssUTZWWgmiqRVMJHi9zJIs8iXUo3xlyGJRUbl7v7sg56/jpOOoUcLCIxyCpjDNoN8et6dpl2W2QEg+9voR0ZHnwbNXr4GE0LxEHno6hAgdcG4VWHugDN+iXH0= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1709041962; c=relaxed/simple; bh=MzCC0AE/rUvpEAo4tb5cVZ7cGsewHKgZszzxyYlWgms=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=Mm6ZPQUvEYWEJ7T9IXqE567dVnRCipA6ACoCMHuEqgvT3NPhRb2zP6XLDUetsTUPKjZTElYOwM3qPcCXAg3ZQNrePvxr1RvMmzXDb69CmMd0zlbh02XTkJbtvNSEVNdVkUNQXbYRWxmjfIchXvVrQwm9CP3DFa+MUxYI38fw2BM= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=i3R9bWJt; arc=none smtp.client-ip=115.124.30.133 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="i3R9bWJt" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1709041958; h=From:To:Subject:Date:Message-Id:MIME-Version; bh=jQS6ixAjVk0AC8cKYwTBDAm2HkLKEDsUdifzfOmBcs0=; b=i3R9bWJt363GKWx5GJRWr6i7VTUoUN3mS7947TEsH0hIcPK9mpi1+rMe+1g2owwUwln/HU+E6tUx4cawEmaXKdIRCNoLh0rkLpUPx8UyCcJaDbTe3bEqJXJkY075nXPZqJzsj3GBiw8iLlmJXH9q9l2GzFLDDFezrn+NrbmgHMs= X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R161e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018045192;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=10;SR=0;TI=SMTPD_---0W1MvL.r_1709041957; Received: from localhost(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0W1MvL.r_1709041957) by smtp.aliyun-inc.com; Tue, 27 Feb 2024 21:52:37 +0800 From: Baolin Wang To: akpm@linux-foundation.org Cc: muchun.song@linux.dev, osalvador@suse.de, david@redhat.com, linmiaohe@huawei.com, naoya.horiguchi@nec.com, mhocko@kernel.org, baolin.wang@linux.alibaba.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH 3/3] docs: hugetlbpage.rst: add hugetlb migration description Date: Tue, 27 Feb 2024 21:52:27 +0800 Message-Id: <574e5bfbaa2b6930aad4a64e1c3da25c4ee5c9ee.1709041586.git.baolin.wang@linux.alibaba.com> X-Mailer: git-send-email 2.39.3 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Add some description of the hugetlb migration strategy. Signed-off-by: Baolin Wang --- Documentation/admin-guide/mm/hugetlbpage.rst | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/Documentation/admin-guide/mm/hugetlbpage.rst b/Documentation/a= dmin-guide/mm/hugetlbpage.rst index e4d4b4a8dc97..f34a0d798d5b 100644 --- a/Documentation/admin-guide/mm/hugetlbpage.rst +++ b/Documentation/admin-guide/mm/hugetlbpage.rst @@ -376,6 +376,13 @@ Note that the number of overcommit and reserve pages r= emain global quantities, as we don't know until fault time, when the faulting task's mempolicy is applied, from which node the huge page allocation will be attempted. =20 +The hugetlb may be migrated between the per-node hugepages pool in the fol= lowing +scenarios: memory offline, memory failure, longterm pinning, syscalls(mbin= d, +migrate_pages and move_pages), alloc_contig_range() and alloc_contig_pages= (). +Now only memory offline, memory failure and syscalls allow fallbacking to = allocate +a new hugetlb on a different node if the current node is unable to allocat= e during +hugetlb migration, that means these 3 cases can break the per-node hugepag= es pool. + .. _using_huge_pages: =20 Using Huge Pages --=20 2.39.3