From nobody Mon Jun 8 19:36:44 2026 Received: from lgeamrelo07.lge.com (lgeamrelo07.lge.com [156.147.51.103]) (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 4928E313520 for ; Wed, 27 May 2026 06:23:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=156.147.51.103 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779863033; cv=none; b=O8XsYHOkoVkP54OIxqmUVAOSsutOKEn4ost/6opyljTkh/gzR3mqF0KrnxTVbI8qPwBKU7VIot763Y7oBgq69INZCYrb98KaM6MYoe1gqxmgZbUsFVQWA7UXMKXBmEvm+se2CBMb8zFL1aNzTkKEM4Su1FWk9IcFBZScL0BDxfI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779863033; c=relaxed/simple; bh=TrBZvQ70KckuhiW870R2slhN6fyBrHtL2uLlW7POmcQ=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=D0DEmHfgs414FNjDUK8Dmm2nI5PK3hKXS2KQR9WwrpG7IJ1fL270O57iyIsJI+sv9ma3lVtcD+8KSBiczfBPrnyOrE5ZOB0Nacz5lpNdfjPuvQrZSPYBIxb7jq1GDO1rdoomzQnFJIoH0drxH9VWhHLblRmYEM+Aeuuy5jfJsBw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=lge.com; spf=pass smtp.mailfrom=lge.com; arc=none smtp.client-ip=156.147.51.103 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=lge.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=lge.com Received: from unknown (HELO yjaykim-PowerEdge-T330.lge.net) (10.177.112.156) by 156.147.51.103 with ESMTP; 27 May 2026 15:23:41 +0900 X-Original-SENDERIP: 10.177.112.156 X-Original-MAILFROM: youngjun.park@lge.com From: Youngjun Park To: akpm@linux-foundation.org Cc: chrisl@kernel.org, youngjun.park@lge.com, linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kasong@tencent.com, hannes@cmpxchg.org, mhocko@kernel.org, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, shikemeng@huaweicloud.com, nphamcs@gmail.com, baoquan.he@linux.dev, baohua@kernel.org, gunho.lee@lge.com, taejoon.song@lge.com, hyungjun.cho@lge.com, mkoutny@suse.com, baver.bae@lge.com, matia.kim@lge.com Subject: [PATCH v7 1/4] mm: swap: introduce swap tier infrastructure Date: Wed, 27 May 2026 15:22:44 +0900 Message-Id: <20260527062247.3440692-2-youngjun.park@lge.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260527062247.3440692-1-youngjun.park@lge.com> References: <20260527062247.3440692-1-youngjun.park@lge.com> 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" This patch introduces the "Swap tier" concept, which serves as an abstraction layer for managing swap devices based on their performance characteristics (e.g., NVMe, HDD, Network swap). Swap tiers are user-named groups representing priority ranges. Tier names must consist of alphanumeric characters and underscores. These tiers collectively cover the entire priority space from -1 (`DEF_SWAP_PRIO`) to `SHRT_MAX`. To configure tiers, a new sysfs interface is exposed at /sys/kernel/mm/swap/tiers. The input parser evaluates commands from left to right and supports batch input, allowing users to add or remove multiple tiers in a single write operation. Tier management enforces continuous priority ranges anchored by start priorities. Operations trigger range splitting or merging, but overwriting start priorities is forbidden. Merging expands lower tiers upwards to preserve configured start priorities, except when removing `DEF_SWAP_PRIO`, which merges downwards. Suggested-by: Chris Li Reviewed-by: Baoquan He Signed-off-by: Youngjun Park --- MAINTAINERS | 2 + mm/Kconfig | 12 ++ mm/Makefile | 2 +- mm/swap.h | 4 + mm/swap_state.c | 74 ++++++++++++ mm/swap_tier.c | 302 ++++++++++++++++++++++++++++++++++++++++++++++++ mm/swap_tier.h | 20 ++++ mm/swapfile.c | 8 +- 8 files changed, 420 insertions(+), 4 deletions(-) create mode 100644 mm/swap_tier.c create mode 100644 mm/swap_tier.h diff --git a/MAINTAINERS b/MAINTAINERS index e3ee97f5474e..e3cbfedbaa5f 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -17049,6 +17049,8 @@ F: mm/swap.c F: mm/swap.h F: mm/swap_table.h F: mm/swap_state.c +F: mm/swap_tier.c +F: mm/swap_tier.h F: mm/swapfile.c =20 MEMORY MANAGEMENT - THP (TRANSPARENT HUGE PAGE) diff --git a/mm/Kconfig b/mm/Kconfig index 776b67c66e82..5343937f3da9 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -19,6 +19,18 @@ menuconfig SWAP used to provide more virtual memory than the actual RAM present in your computer. If unsure say Y. =20 +config NR_SWAP_TIERS + int "Number of swap device tiers" + depends on SWAP + default 4 + range 1 31 + help + Sets the number of swap device tiers. Swap devices are + grouped into tiers based on their priority, allowing the + system to prefer faster devices over slower ones. + + If unsure, say 4. + config ZSWAP bool "Compressed cache for swap pages" depends on SWAP diff --git a/mm/Makefile b/mm/Makefile index eff9f9e7e061..29cb1e778285 100644 --- a/mm/Makefile +++ b/mm/Makefile @@ -75,7 +75,7 @@ ifdef CONFIG_MMU obj-$(CONFIG_ADVISE_SYSCALLS) +=3D madvise.o endif =20 -obj-$(CONFIG_SWAP) +=3D page_io.o swap_state.o swapfile.o +obj-$(CONFIG_SWAP) +=3D page_io.o swap_state.o swapfile.o swap_tier.o obj-$(CONFIG_ZSWAP) +=3D zswap.o obj-$(CONFIG_HAS_DMA) +=3D dmapool.o obj-$(CONFIG_HUGETLBFS) +=3D hugetlb.o hugetlb_sysfs.o hugetlb_sysctl.o diff --git a/mm/swap.h b/mm/swap.h index 900a539c63f0..067f0afd7a3e 100644 --- a/mm/swap.h +++ b/mm/swap.h @@ -34,6 +34,10 @@ extern int page_cluster; #define swap_entry_order(order) 0 #endif =20 +#define DEF_SWAP_PRIO -1 + +extern spinlock_t swap_lock; +extern struct plist_head swap_active_head; extern struct swap_info_struct *swap_info[]; =20 /* diff --git a/mm/swap_state.c b/mm/swap_state.c index 04f5ce992401..e609bbdf7e13 100644 --- a/mm/swap_state.c +++ b/mm/swap_state.c @@ -25,6 +25,7 @@ #include "internal.h" #include "swap_table.h" #include "swap.h" +#include "swap_tier.h" =20 /* * swapper_space is a fiction, retained to simplify the path through @@ -997,8 +998,81 @@ static ssize_t vma_ra_enabled_store(struct kobject *ko= bj, } static struct kobj_attribute vma_ra_enabled_attr =3D __ATTR_RW(vma_ra_enab= led); =20 +static ssize_t tiers_show(struct kobject *kobj, + struct kobj_attribute *attr, char *buf) +{ + return swap_tiers_sysfs_show(buf); +} + +static ssize_t tiers_store(struct kobject *kobj, + struct kobj_attribute *attr, + const char *buf, size_t count) +{ + char *p, *token, *name, *tmp; + int ret =3D 0; + short prio; + + tmp =3D kstrdup(buf, GFP_KERNEL); + if (!tmp) + return -ENOMEM; + + spin_lock(&swap_lock); + spin_lock(&swap_tier_lock); + swap_tiers_snapshot(); + + p =3D tmp; + while ((token =3D strsep(&p, ", \t\n")) !=3D NULL) { + if (!*token) + continue; + + switch (token[0]) { + case '+': + name =3D token + 1; + token =3D strchr(name, ':'); + if (!token) { + ret =3D -EINVAL; + goto restore; + } + *token++ =3D '\0'; + if (kstrtos16(token, 10, &prio)) { + ret =3D -EINVAL; + goto restore; + } + ret =3D swap_tiers_add(name, prio); + if (ret) + goto restore; + break; + case '-': + ret =3D swap_tiers_remove(token + 1); + if (ret) + goto restore; + break; + default: + ret =3D -EINVAL; + goto restore; + } + } + + if (!swap_tiers_validate()) { + ret =3D -EINVAL; + goto restore; + } + goto out; + +restore: + swap_tiers_snapshot_restore(); +out: + spin_unlock(&swap_tier_lock); + spin_unlock(&swap_lock); + kfree(tmp); + return ret ? ret : count; +} + +static struct kobj_attribute tier_attr =3D __ATTR_RW(tiers); + static struct attribute *swap_attrs[] =3D { &vma_ra_enabled_attr.attr, + &tier_attr.attr, NULL, }; =20 diff --git a/mm/swap_tier.c b/mm/swap_tier.c new file mode 100644 index 000000000000..ac7a3c2a48cb --- /dev/null +++ b/mm/swap_tier.c @@ -0,0 +1,302 @@ +// SPDX-License-Identifier: GPL-2.0 +#include +#include +#include "memcontrol-v1.h" +#include +#include + +#include "swap.h" +#include "swap_tier.h" + +#define MAX_SWAPTIER CONFIG_NR_SWAP_TIERS +#define MAX_TIERNAME 16 + +/* + * struct swap_tier - structure representing a swap tier. + * + * @name: name of the swap_tier. + * @prio: starting value of priority. + * @list: linked list of tiers. + */ +static struct swap_tier { + char name[MAX_TIERNAME]; + short prio; + struct list_head list; +} swap_tiers[MAX_SWAPTIER]; + +DEFINE_SPINLOCK(swap_tier_lock); +/* active swap priority list, sorted in descending order */ +static LIST_HEAD(swap_tier_active_list); +/* unused swap_tier object */ +static LIST_HEAD(swap_tier_inactive_list); + +#define TIER_IDX(tier) ((tier) - swap_tiers) +#define TIER_MASK(tier) (1U << TIER_IDX(tier)) +#define TIER_INACTIVE_PRIO (DEF_SWAP_PRIO - 1) +#define TIER_IS_ACTIVE(tier) ((tier->prio) !=3D TIER_INACTIVE_PRIO) +#define TIER_END_PRIO(tier) \ + (!list_is_first(&(tier)->list, &swap_tier_active_list) ? \ + list_prev_entry((tier), list)->prio - 1 : SHRT_MAX) + +#define for_each_tier(tier, idx) \ + for (idx =3D 0, tier =3D &swap_tiers[0]; idx < MAX_SWAPTIER; \ + idx++, tier =3D &swap_tiers[idx]) + +#define for_each_active_tier(tier) \ + list_for_each_entry(tier, &swap_tier_active_list, list) + +#define for_each_inactive_tier(tier) \ + list_for_each_entry(tier, &swap_tier_inactive_list, list) + +/* + * Naming Convention: + * swap_tiers_*() - Public/exported functions + * swap_tier_*() - Private/internal functions + */ + +static bool swap_tier_is_active(void) +{ + return !list_empty(&swap_tier_active_list); +} + +static struct swap_tier *swap_tier_lookup(const char *name) +{ + struct swap_tier *tier; + + for_each_active_tier(tier) { + if (!strcmp(tier->name, name)) + return tier; + } + + return NULL; +} + +/* Insert new tier into the active list sorted by priority. */ +static void swap_tier_activate(struct swap_tier *new) +{ + struct list_head *pos =3D &swap_tier_active_list; + struct swap_tier *tier; + + for_each_active_tier(tier) { + if (tier->prio <=3D new->prio) { + pos =3D &tier->list; + break; + } + } + + list_add_tail(&new->list, pos); +} + +static void swap_tier_inactivate(struct swap_tier *tier) +{ + list_move(&tier->list, &swap_tier_inactive_list); + tier->prio =3D TIER_INACTIVE_PRIO; +} + +void swap_tiers_init(void) +{ + struct swap_tier *tier; + int idx; + + BUILD_BUG_ON(BITS_PER_TYPE(int) < MAX_SWAPTIER); + + for_each_tier(tier, idx) { + INIT_LIST_HEAD(&tier->list); + swap_tier_inactivate(tier); + } +} + +ssize_t swap_tiers_sysfs_show(char *buf) +{ + struct swap_tier *tier; + ssize_t len =3D 0; + + len +=3D sysfs_emit_at(buf, len, "%-16s %-5s %-11s %-11s\n", + "Name", "Idx", "PrioStart", "PrioEnd"); + + spin_lock(&swap_tier_lock); + for_each_active_tier(tier) { + len +=3D sysfs_emit_at(buf, len, "%-16s %-5td %-11d %-11d\n", + tier->name, + TIER_IDX(tier), + tier->prio, + TIER_END_PRIO(tier)); + } + spin_unlock(&swap_tier_lock); + + return len; +} + +static struct swap_tier *swap_tier_prepare(const char *name, short prio) +{ + struct swap_tier *tier; + + lockdep_assert_held(&swap_tier_lock); + + if (prio < DEF_SWAP_PRIO) + return ERR_PTR(-EINVAL); + + if (list_empty(&swap_tier_inactive_list)) + return ERR_PTR(-ENOSPC); + + tier =3D list_first_entry(&swap_tier_inactive_list, + struct swap_tier, list); + + list_del_init(&tier->list); + strscpy(tier->name, name, MAX_TIERNAME); + tier->prio =3D prio; + + return tier; +} + +static int swap_tier_check_range(short prio) +{ + struct swap_tier *tier; + + lockdep_assert_held(&swap_lock); + lockdep_assert_held(&swap_tier_lock); + + for_each_active_tier(tier) { + /* No overwrite */ + if (tier->prio =3D=3D prio) + return -EINVAL; + } + + return 0; +} + +static bool swap_tier_validate_name(const char *name) +{ + int len; + + if (!name || !*name) + return false; + + len =3D strlen(name); + if (len >=3D MAX_TIERNAME) + return false; + + while (*name) { + if (!isalnum(*name) && *name !=3D '_') + return false; + name++; + } + return true; +} + +int swap_tiers_add(const char *name, int prio) +{ + int ret; + struct swap_tier *tier; + + lockdep_assert_held(&swap_lock); + lockdep_assert_held(&swap_tier_lock); + + /* Duplicate check */ + if (swap_tier_lookup(name)) + return -EEXIST; + + if (!swap_tier_validate_name(name)) + return -EINVAL; + + ret =3D swap_tier_check_range(prio); + if (ret) + return ret; + + tier =3D swap_tier_prepare(name, prio); + if (IS_ERR(tier)) { + ret =3D PTR_ERR(tier); + return ret; + } + + swap_tier_activate(tier); + + return ret; +} + +int swap_tiers_remove(const char *name) +{ + int ret =3D 0; + struct swap_tier *tier; + + lockdep_assert_held(&swap_lock); + lockdep_assert_held(&swap_tier_lock); + + tier =3D swap_tier_lookup(name); + if (!tier) + return -EINVAL; + + /* Removing DEF_SWAP_PRIO merges into the higher tier. */ + if (!list_is_singular(&swap_tier_active_list) + && tier->prio =3D=3D DEF_SWAP_PRIO) + list_prev_entry(tier, list)->prio =3D DEF_SWAP_PRIO; + + swap_tier_inactivate(tier); + + return ret; +} + +static struct swap_tier swap_tiers_snap[MAX_SWAPTIER]; +/* + * XXX: When multiple operations (adds and removes) are submitted in a + * single write, reverting each individually on failure is complex and + * error-prone. Instead, snapshot the entire state beforehand and + * restore it wholesale if any operation fails. + */ +void swap_tiers_snapshot(void) +{ + BUILD_BUG_ON(sizeof(swap_tiers_snap) !=3D sizeof(swap_tiers)); + + lockdep_assert_held(&swap_lock); + lockdep_assert_held(&swap_tier_lock); + + memcpy(swap_tiers_snap, swap_tiers, sizeof(swap_tiers)); +} + +void swap_tiers_snapshot_restore(void) +{ + struct swap_tier *tier; + int idx; + + lockdep_assert_held(&swap_lock); + lockdep_assert_held(&swap_tier_lock); + + memcpy(swap_tiers, swap_tiers_snap, sizeof(swap_tiers)); + + INIT_LIST_HEAD(&swap_tier_active_list); + INIT_LIST_HEAD(&swap_tier_inactive_list); + + /* + * memcpy copied snapshot-time list pointers into each tier's + * list_head. Those references are stale, so re-init every + * tier before re-linking into the freshly initialised global + * lists below. + */ + for_each_tier(tier, idx) { + INIT_LIST_HEAD(&tier->list); + + if (TIER_IS_ACTIVE(tier)) + swap_tier_activate(tier); + else + swap_tier_inactivate(tier); + } +} + +bool swap_tiers_validate(void) +{ + struct swap_tier *tier; + + /* + * Initial setting might not cover DEF_SWAP_PRIO. + * Swap tier must cover the full range (DEF_SWAP_PRIO to SHRT_MAX). + */ + if (swap_tier_is_active()) { + tier =3D list_last_entry(&swap_tier_active_list, + struct swap_tier, list); + + if (tier->prio !=3D DEF_SWAP_PRIO) + return false; + } + + return true; +} diff --git a/mm/swap_tier.h b/mm/swap_tier.h new file mode 100644 index 000000000000..a1395ec02c24 --- /dev/null +++ b/mm/swap_tier.h @@ -0,0 +1,20 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _SWAP_TIER_H +#define _SWAP_TIER_H + +#include +#include + +extern spinlock_t swap_tier_lock; + +/* Initialization and application */ +void swap_tiers_init(void); +ssize_t swap_tiers_sysfs_show(char *buf); + +int swap_tiers_add(const char *name, int prio); +int swap_tiers_remove(const char *name); + +void swap_tiers_snapshot(void); +void swap_tiers_snapshot_restore(void); +bool swap_tiers_validate(void); +#endif /* _SWAP_TIER_H */ diff --git a/mm/swapfile.c b/mm/swapfile.c index e3d126602a1e..3f7225dbc6cd 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -48,6 +48,7 @@ #include "swap_table.h" #include "internal.h" #include "swap.h" +#include "swap_tier.h" =20 static void swap_range_alloc(struct swap_info_struct *si, unsigned int nr_entries); @@ -63,7 +64,8 @@ static void move_cluster(struct swap_info_struct *si, * * Also protects swap_active_head total_swap_pages, and the SWP_WRITEOK fl= ag. */ -static DEFINE_SPINLOCK(swap_lock); +DEFINE_SPINLOCK(swap_lock); + static unsigned int nr_swapfiles; atomic_long_t nr_swap_pages; /* @@ -74,7 +76,6 @@ atomic_long_t nr_swap_pages; EXPORT_SYMBOL_GPL(nr_swap_pages); /* protected with swap_lock. reading in vm_swap_full() doesn't need lock */ long total_swap_pages; -#define DEF_SWAP_PRIO -1 unsigned long swapfile_maximum_size; #ifdef CONFIG_MIGRATION bool swap_migration_ad_supported; @@ -87,7 +88,7 @@ static const char Bad_offset[] =3D "Bad swap offset entry= "; * all active swap_info_structs * protected with swap_lock, and ordered by priority. */ -static PLIST_HEAD(swap_active_head); +PLIST_HEAD(swap_active_head); =20 /* * all available (active, not full) swap_info_structs @@ -3988,6 +3989,7 @@ static int __init swapfile_init(void) swap_migration_ad_supported =3D true; #endif /* CONFIG_MIGRATION */ =20 + swap_tiers_init(); return 0; } subsys_initcall(swapfile_init); --=20 2.34.1 From nobody Mon Jun 8 19:36:44 2026 Received: from lgeamrelo07.lge.com (lgeamrelo07.lge.com [156.147.51.103]) (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 5F9E1311973 for ; Wed, 27 May 2026 06:23:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; 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spf=pass smtp.mailfrom=lge.com Received: from unknown (HELO yjaykim-PowerEdge-T330.lge.net) (10.177.112.156) by 156.147.51.103 with ESMTP; 27 May 2026 15:23:44 +0900 X-Original-SENDERIP: 10.177.112.156 X-Original-MAILFROM: youngjun.park@lge.com From: Youngjun Park To: akpm@linux-foundation.org Cc: chrisl@kernel.org, youngjun.park@lge.com, linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kasong@tencent.com, hannes@cmpxchg.org, mhocko@kernel.org, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, shikemeng@huaweicloud.com, nphamcs@gmail.com, baoquan.he@linux.dev, baohua@kernel.org, gunho.lee@lge.com, taejoon.song@lge.com, hyungjun.cho@lge.com, mkoutny@suse.com, baver.bae@lge.com, matia.kim@lge.com Subject: [PATCH v7 2/4] mm: swap: associate swap devices with tiers Date: Wed, 27 May 2026 15:22:45 +0900 Message-Id: <20260527062247.3440692-3-youngjun.park@lge.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260527062247.3440692-1-youngjun.park@lge.com> References: <20260527062247.3440692-1-youngjun.park@lge.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable This patch connects swap devices to the swap tier infrastructure, ensuring that devices are correctly assigned to tiers based on their priority. A `tier_mask` is added to identify the tier membership of swap devices. Although tier-based allocation logic is not yet implemented, this mapping is necessary to track which tier a device belongs to. Upon activation, the device is assigned to a tier by matching its priority against the configured tier ranges. The infrastructure allows dynamic modification of tiers, such as splitting or merging ranges. These operations are permitted provided that the tier assignment of already configured swap devices remains unchanged. This patch also adds the documentation for the swap tier feature, covering the core concepts, sysfs interface usage, and configuration details. Reviewed-by: Baoquan He Signed-off-by: Youngjun Park --- Documentation/mm/index.rst | 1 + Documentation/mm/swap-tier.rst | 159 +++++++++++++++++++++++++++++++++ MAINTAINERS | 1 + include/linux/swap.h | 1 + mm/swap_state.c | 2 +- mm/swap_tier.c | 101 ++++++++++++++++++--- mm/swap_tier.h | 13 ++- mm/swapfile.c | 2 + 8 files changed, 266 insertions(+), 14 deletions(-) create mode 100644 Documentation/mm/swap-tier.rst diff --git a/Documentation/mm/index.rst b/Documentation/mm/index.rst index 7aa2a8886908..a0d1447c5569 100644 --- a/Documentation/mm/index.rst +++ b/Documentation/mm/index.rst @@ -21,6 +21,7 @@ see the :doc:`admin guide <../admin-guide/mm/index>`. page_reclaim swap swap-table + swap-tier page_cache shmfs oom diff --git a/Documentation/mm/swap-tier.rst b/Documentation/mm/swap-tier.rst new file mode 100644 index 000000000000..addbc495de8c --- /dev/null +++ b/Documentation/mm/swap-tier.rst @@ -0,0 +1,159 @@ +.. SPDX-License-Identifier: GPL-2.0 + +:Author: Chris Li Youngjun Park + +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D +Swap Tier +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D + +Swap tier is a collection of user-named groups classified by priority rang= es. +It acts as a facilitation layer, allowing users to manage swap devices bas= ed +on their speeds. + +Users are encouraged to assign swap device priorities according to device +speed to fully utilize this feature. While the current implementation is +integrated with cgroups, the concept is designed to be extensible for other +subsystems in the future. + +Use case +--------- + +Users can perform selective swapping by choosing a swap tier assigned acco= rding +to speed within a cgroup. + +For more information on cgroup v2, please refer to +``Documentation/admin-guide/cgroup-v2.rst``. + +Priority Range +-------------- + +The specified tiers must cover the entire priority range from -1 +(DEF_SWAP_PRIO) to SHRT_MAX. + +Consistency +----------- + +Tier consistency is guaranteed with a focus on maximizing flexibility. Whe= n a +swap device is activated within a tier range, the tier covering that devic= e's +priority is guaranteed not to disappear or change while the device remains +active. Adding a new tier may split the range of an existing tier, but the +active device's tier assignment remains unchanged. + +However, specifying a tier in a cgroup does not guarantee the tier's exist= ence. +Consequently, the corresponding tier can disappear at any time. + +Configuration Interface +----------------------- + +The swap tiers can be configured via the following interface: + +/sys/kernel/mm/swap/tiers + +Operations can be performed using the following syntax: + +* Add: ``+"":""`` +* Remove: ``-""`` + +Tier names must consist of alphanumeric characters and underscores. Multip= le +operations can be provided in a single write, separated by commas (",") or +whitespace (spaces, tabs, newlines). + +When configuring tiers, the specified value represents the **start priorit= y** +of that tier. The end priority is automatically determined by the start +priority of the next higher tier. Consequently, adding a tier +automatically adjusts the ranges of adjacent tiers to ensure continuity. + +Examples +-------- + +**1. Initialization** + +A tier starting at -1 is mandatory to cover the entire priority range up to +SHRT_MAX. In this example, 'HDD' starts at 50, and 'NET' covers the remain= ing +lower range starting from -1. + +:: + + # echo "+HDD:50, +NET:-1" > /sys/kernel/mm/swap/tiers + # cat /sys/kernel/mm/swap/tiers + Name Idx PrioStart PrioEnd + HDD 0 50 32767 + NET 1 -1 49 + +**2. Adding a New Tier (split)** + +A new tier 'SSD' is added at priority 100, splitting the existing 'HDD' ti= er. +The ranges are automatically recalculated: + +* 'SSD' takes the top range (100 to SHRT_MAX). +* 'HDD' is adjusted to the range between 'NET' and 'SSD' (50 to 99). +* 'NET' remains unchanged (-1 to 49). + +:: + + # echo "+SSD:100" > /sys/kernel/mm/swap/tiers + # cat /sys/kernel/mm/swap/tiers + Name Idx PrioStart PrioEnd + SSD 2 100 32767 + HDD 0 50 99 + NET 1 -1 49 + +**3. Removal (merge)** + +Tiers can be removed using the '-' prefix. +:: + + # echo "-SSD" > /sys/kernel/mm/swap/tiers + +When a tier is removed, its priority range is merged into the adjacent +tier. The merge direction is always upward (the tier below expands), +except when the lowest tier is removed =E2=80=94 in that case the tier abo= ve +shifts its starting priority down to -1 to maintain full range coverage. + +:: + + Initial state: + Name Idx PrioStart PrioEnd + SSD 2 100 32767 + HDD 1 50 99 + NET 0 -1 49 + + # echo "-SSD" > /sys/kernel/mm/swap/tiers + + Name Idx PrioStart PrioEnd + HDD 1 50 32767 <- merged with SSD's ra= nge + NET 0 -1 49 + + # echo "-NET" > /sys/kernel/mm/swap/tiers + + Name Idx PrioStart PrioEnd + HDD 1 -1 32767 <- shifted down to -1 + +**4. Interaction with Active Swap Devices** + +If a swap device is active (swapon), the tier covering that device's +priority cannot be removed. Splitting the active tier's range is only +allowed above the device's priority. + +Assume a swap device is active at priority 60 (inside 'HDD' tier). + +:: + + # swapon -p 60 /dev/zram0 + + Name Idx PrioStart PrioEnd + HDD 0 50 32767 + NET 1 -1 49 + + # echo "-HDD" > /sys/kernel/mm/swap/tiers + -bash: echo: write error: Device or resource busy + + # echo "+SSD:60" > /sys/kernel/mm/swap/tiers + -bash: echo: write error: Device or resource busy + + # echo "+SSD:100" > /sys/kernel/mm/swap/tiers + + Name Idx PrioStart PrioEnd + SSD 2 100 32767 + HDD 0 50 99 <- device (prio 60) sta= ys here + NET 1 -1 49 diff --git a/MAINTAINERS b/MAINTAINERS index e3cbfedbaa5f..c008014663b3 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -17041,6 +17041,7 @@ R: Youngjun Park L: linux-mm@kvack.org S: Maintained F: Documentation/mm/swap-table.rst +F: Documentation/mm/swap-tier.rst F: include/linux/swap.h F: include/linux/swapfile.h F: include/linux/swapops.h diff --git a/include/linux/swap.h b/include/linux/swap.h index 6d72778e6cc3..21286945770a 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -250,6 +250,7 @@ struct swap_info_struct { struct percpu_ref users; /* indicate and keep swap device valid. */ unsigned long flags; /* SWP_USED etc: see above */ signed short prio; /* swap priority of this type */ + int tier_mask; /* swap tier mask */ struct plist_node list; /* entry in swap_active_head */ signed char type; /* strange name for an index */ unsigned int max; /* size of this swap device */ diff --git a/mm/swap_state.c b/mm/swap_state.c index e609bbdf7e13..de285b36e31c 100644 --- a/mm/swap_state.c +++ b/mm/swap_state.c @@ -1053,7 +1053,7 @@ static ssize_t tiers_store(struct kobject *kobj, } } =20 - if (!swap_tiers_validate()) { + if (!swap_tiers_update()) { ret =3D -EINVAL; goto restore; } diff --git a/mm/swap_tier.c b/mm/swap_tier.c index ac7a3c2a48cb..6b57cadb3e95 100644 --- a/mm/swap_tier.c +++ b/mm/swap_tier.c @@ -38,6 +38,8 @@ static LIST_HEAD(swap_tier_inactive_list); (!list_is_first(&(tier)->list, &swap_tier_active_list) ? \ list_prev_entry((tier), list)->prio - 1 : SHRT_MAX) =20 +#define MASK_TO_TIER(mask) (&swap_tiers[__ffs((mask))]) + #define for_each_tier(tier, idx) \ for (idx =3D 0, tier =3D &swap_tiers[0]; idx < MAX_SWAPTIER; \ idx++, tier =3D &swap_tiers[idx]) @@ -59,6 +61,26 @@ static bool swap_tier_is_active(void) return !list_empty(&swap_tier_active_list); } =20 +static bool swap_tier_prio_in_range(struct swap_tier *tier, short prio) +{ + if (tier->prio <=3D prio && TIER_END_PRIO(tier) >=3D prio) + return true; + + return false; +} + +static bool swap_tier_prio_is_used(short prio) +{ + struct swap_tier *tier; + + for_each_active_tier(tier) { + if (tier->prio =3D=3D prio) + return true; + } + + return false; +} + static struct swap_tier *swap_tier_lookup(const char *name) { struct swap_tier *tier; @@ -99,6 +121,7 @@ void swap_tiers_init(void) int idx; =20 BUILD_BUG_ON(BITS_PER_TYPE(int) < MAX_SWAPTIER); + BUILD_BUG_ON(MAX_SWAPTIER > TIER_DEFAULT_IDX); =20 for_each_tier(tier, idx) { INIT_LIST_HEAD(&tier->list); @@ -149,17 +172,29 @@ static struct swap_tier *swap_tier_prepare(const char= *name, short prio) return tier; } =20 -static int swap_tier_check_range(short prio) +static int swap_tier_can_split_range(short new_prio) { + struct swap_info_struct *p; struct swap_tier *tier; =20 lockdep_assert_held(&swap_lock); lockdep_assert_held(&swap_tier_lock); =20 - for_each_active_tier(tier) { - /* No overwrite */ - if (tier->prio =3D=3D prio) - return -EINVAL; + plist_for_each_entry(p, &swap_active_head, list) { + if (p->tier_mask =3D=3D TIER_DEFAULT_MASK) + continue; + + tier =3D MASK_TO_TIER(p->tier_mask); + if (!swap_tier_prio_in_range(tier, new_prio)) + continue; + + /* + * Device sits in a tier that spans new_prio; + * splitting here would reassign it to a + * different tier. + */ + if (p->prio >=3D new_prio) + return -EBUSY; } =20 return 0; @@ -199,7 +234,11 @@ int swap_tiers_add(const char *name, int prio) if (!swap_tier_validate_name(name)) return -EINVAL; =20 - ret =3D swap_tier_check_range(prio); + /* No overwrite */ + if (swap_tier_prio_is_used(prio)) + return -EBUSY; + + ret =3D swap_tier_can_split_range(prio); if (ret) return ret; =20 @@ -226,6 +265,11 @@ int swap_tiers_remove(const char *name) if (!tier) return -EINVAL; =20 + /* Simulate adding a tier to check for conflicts */ + ret =3D swap_tier_can_split_range(tier->prio); + if (ret) + return ret; + /* Removing DEF_SWAP_PRIO merges into the higher tier. */ if (!list_is_singular(&swap_tier_active_list) && tier->prio =3D=3D DEF_SWAP_PRIO) @@ -236,13 +280,15 @@ int swap_tiers_remove(const char *name) return ret; } =20 -static struct swap_tier swap_tiers_snap[MAX_SWAPTIER]; /* - * XXX: When multiple operations (adds and removes) are submitted in a - * single write, reverting each individually on failure is complex and - * error-prone. Instead, snapshot the entire state beforehand and - * restore it wholesale if any operation fails. + * XXX: Static global snapshot buffer for batch operations. Small + * and used once per write, so a static global is not bad. + * When multiple adds/removes are submitted in a single write, + * reverting each individually on failure is error-prone. Instead, + * snapshot beforehand and restore wholesale if any operation fails. */ +static struct swap_tier swap_tiers_snap[MAX_SWAPTIER]; + void swap_tiers_snapshot(void) { BUILD_BUG_ON(sizeof(swap_tiers_snap) !=3D sizeof(swap_tiers)); @@ -282,10 +328,30 @@ void swap_tiers_snapshot_restore(void) } } =20 -bool swap_tiers_validate(void) +void swap_tiers_assign_dev(struct swap_info_struct *swp) { struct swap_tier *tier; =20 + lockdep_assert_held(&swap_lock); + + for_each_active_tier(tier) { + if (swap_tier_prio_in_range(tier, swp->prio)) { + swp->tier_mask =3D TIER_MASK(tier); + return; + } + } + + swp->tier_mask =3D TIER_DEFAULT_MASK; +} + +bool swap_tiers_update(void) +{ + struct swap_tier *tier; + struct swap_info_struct *swp; + + lockdep_assert_held(&swap_lock); + lockdep_assert_held(&swap_tier_lock); + /* * Initial setting might not cover DEF_SWAP_PRIO. * Swap tier must cover the full range (DEF_SWAP_PRIO to SHRT_MAX). @@ -298,5 +364,16 @@ bool swap_tiers_validate(void) return false; } =20 + /* + * If applied initially, the swap tier_mask may change + * from the default value. + */ + plist_for_each_entry(swp, &swap_active_head, list) { + /* Tier is already configured */ + if (swp->tier_mask !=3D TIER_DEFAULT_MASK) + break; + swap_tiers_assign_dev(swp); + } + return true; } diff --git a/mm/swap_tier.h b/mm/swap_tier.h index a1395ec02c24..3e355f857363 100644 --- a/mm/swap_tier.h +++ b/mm/swap_tier.h @@ -5,8 +5,15 @@ #include #include =20 +/* Forward declarations */ +struct swap_info_struct; + extern spinlock_t swap_tier_lock; =20 +#define TIER_ALL_MASK (~0) +#define TIER_DEFAULT_IDX (31) +#define TIER_DEFAULT_MASK (1U << TIER_DEFAULT_IDX) + /* Initialization and application */ void swap_tiers_init(void); ssize_t swap_tiers_sysfs_show(char *buf); @@ -16,5 +23,9 @@ int swap_tiers_remove(const char *name); =20 void swap_tiers_snapshot(void); void swap_tiers_snapshot_restore(void); -bool swap_tiers_validate(void); +bool swap_tiers_update(void); + +/* Tier assignment */ +void swap_tiers_assign_dev(struct swap_info_struct *swp); + #endif /* _SWAP_TIER_H */ diff --git a/mm/swapfile.c b/mm/swapfile.c index 3f7225dbc6cd..9a86ebe992f4 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -3036,6 +3036,8 @@ static void _enable_swap_info(struct swap_info_struct= *si) =20 /* Add back to available list */ add_to_avail_list(si, true); + + swap_tiers_assign_dev(si); } =20 /* --=20 2.34.1 From nobody Mon Jun 8 19:36:44 2026 Received: from lgeamrelo07.lge.com (lgeamrelo07.lge.com [156.147.51.103]) (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 2523131355D for ; Wed, 27 May 2026 06:23:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=156.147.51.103 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779863032; cv=none; b=Ryg2z0qc6GDPNXw98H6S+N12blDGU4lNTHR6qhXs8vw+estroqmsZn5WqssvACDdTPlmYUxGBfkz6uZqoGVqA2oGTNR+vOIbW8CSP1OLEsNCsLruvq4RwwT9bhsPYT87VmfNH/6QJPGEq04JFlhBc79P861Eg+LuePGhiqe11HA= ARC-Message-Signature: i=1; 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charset="utf-8" Integrate swap tier infrastructure with cgroup to allow selecting specific swap devices per cgroup. Introduce memory.swap.tiers for configuring allowed tiers, and memory.swap.tiers.effective for exposing the effective tiers. The effective tiers are the intersection of the configured tiers and the parent's effective tiers. Note that cgroups do not pin swap tiers, similar to cpuset and CPU hotplug, allowing configuration changes regardless of usage. Signed-off-by: Youngjun Park --- Documentation/admin-guide/cgroup-v2.rst | 29 +++++++ include/linux/memcontrol.h | 5 ++ mm/memcontrol.c | 96 +++++++++++++++++++++ mm/swap_state.c | 5 +- mm/swap_tier.c | 107 +++++++++++++++++++++++- mm/swap_tier.h | 56 +++++++++++-- 6 files changed, 288 insertions(+), 10 deletions(-) diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-= guide/cgroup-v2.rst index 6efd0095ed99..08253072a252 100644 --- a/Documentation/admin-guide/cgroup-v2.rst +++ b/Documentation/admin-guide/cgroup-v2.rst @@ -1850,6 +1850,35 @@ The following nested keys are defined. Swap usage hard limit. If a cgroup's swap usage reaches this limit, anonymous memory of the cgroup will not be swapped out. =20 + memory.swap.tiers + A read-write file which exists on non-root cgroups. + Format is similar to cgroup.subtree_control. + + Controls which swap tiers this cgroup is allowed to swap + out to. All tiers are enabled by default. + + :: + + (-|+)TIER [(-|+)TIER ...] + + "-" disables a tier, "+" re-enables it. + Entries are whitespace-delimited. + + Changes here are combined with parent restrictions to + compute memory.swap.tiers.effective. + + If a tier is removed from /sys/kernel/mm/swap/tiers, + any prior disable for that tier is invalidated. + + memory.swap.tiers.effective + A read-only file which exists on non-root cgroups. + + Shows the tiers this cgroup can actually swap out to. + This is the intersection of the parent's effective tiers + and this cgroup's own memory.swap.tiers configuration. + A child cannot enable a tier that is disabled in its + parent. + memory.swap.events A read-only flat-keyed file which exists on non-root cgroups. The following entries are defined. Unless specified diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index bf1a6e131eca..eb33c8e30c9e 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -287,6 +287,11 @@ struct mem_cgroup { struct lru_gen_mm_list mm_list; #endif =20 +#ifdef CONFIG_SWAP + int tier_mask; + int tier_effective_mask; +#endif + #ifdef CONFIG_MEMCG_V1 /* Legacy consumer-oriented counters */ struct page_counter kmem; /* v1 only */ diff --git a/mm/memcontrol.c b/mm/memcontrol.c index e24114a4493a..cbc7a519a24d 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -68,6 +68,7 @@ #include #include "slab.h" #include "memcontrol-v1.h" +#include "swap_tier.h" =20 #include =20 @@ -4249,6 +4250,8 @@ static int mem_cgroup_css_online(struct cgroup_subsys= _state *css) refcount_set(&memcg->id.ref, 1); css_get(css); =20 + swap_tiers_memcg_inherit_mask(memcg); + /* * Ensure mem_cgroup_from_private_id() works once we're fully online. * @@ -5791,6 +5794,88 @@ static int swap_events_show(struct seq_file *m, void= *v) return 0; } =20 +static int swap_tier_show(struct seq_file *m, void *v) +{ + struct mem_cgroup *memcg =3D mem_cgroup_from_seq(m); + + swap_tiers_mask_show(m, READ_ONCE(memcg->tier_mask)); + return 0; +} + +static ssize_t swap_tier_write(struct kernfs_open_file *of, + char *buf, size_t nbytes, loff_t off) +{ + struct mem_cgroup *memcg =3D mem_cgroup_from_css(of_css(of)); + char *pos, *token; + int ret =3D 0; + int original_mask =3D 0; + + pos =3D strstrip(buf); + + spin_lock(&swap_tier_lock); + if (!*pos) { + WRITE_ONCE(memcg->tier_mask, TIER_ALL_MASK); + goto sync; + } + + original_mask =3D memcg->tier_mask; + + while ((token =3D strsep(&pos, " \t\n")) !=3D NULL) { + int mask; + + if (!*token) + continue; + + if (token[0] !=3D '-' && token[0] !=3D '+') { + ret =3D -EINVAL; + goto err; + } + + mask =3D swap_tiers_mask_lookup(token+1); + if (!mask) { + ret =3D -EINVAL; + goto err; + } + /* + * tier_mask can be modified independently at each memcg. + * However, the effective mask is restricted to a subset of + * the parent's mask in swap_tiers_memcg_sync_mask(). + */ + switch (token[0]) { + case '-': + WRITE_ONCE(memcg->tier_mask, + memcg->tier_mask & ~mask); + break; + case '+': + WRITE_ONCE(memcg->tier_mask, + memcg->tier_mask | mask); + break; + default: + ret =3D -EINVAL; + break; + } + + if (ret) + goto err; + } + +sync: + swap_tiers_memcg_sync_mask(memcg); +err: + if (ret) + WRITE_ONCE(memcg->tier_mask, original_mask); + spin_unlock(&swap_tier_lock); + return ret ? ret : nbytes; +} + +static int swap_tier_effective_show(struct seq_file *m, void *v) +{ + struct mem_cgroup *memcg =3D mem_cgroup_from_seq(m); + + swap_tiers_mask_show(m, READ_ONCE(memcg->tier_effective_mask)); + return 0; +} + static struct cftype swap_files[] =3D { { .name =3D "swap.current", @@ -5823,6 +5908,17 @@ static struct cftype swap_files[] =3D { .file_offset =3D offsetof(struct mem_cgroup, swap_events_file), .seq_show =3D swap_events_show, }, + { + .name =3D "swap.tiers", + .flags =3D CFTYPE_NOT_ON_ROOT, + .seq_show =3D swap_tier_show, + .write =3D swap_tier_write, + }, + { + .name =3D "swap.tiers.effective", + .flags =3D CFTYPE_NOT_ON_ROOT, + .seq_show =3D swap_tier_effective_show, + }, { } /* terminate */ }; =20 diff --git a/mm/swap_state.c b/mm/swap_state.c index de285b36e31c..2fda6b61e2de 100644 --- a/mm/swap_state.c +++ b/mm/swap_state.c @@ -1011,6 +1011,7 @@ static ssize_t tiers_store(struct kobject *kobj, char *p, *token, *name, *tmp; int ret =3D 0; short prio; + int mask =3D 0; =20 tmp =3D kstrdup(buf, GFP_KERNEL); if (!tmp) @@ -1043,7 +1044,7 @@ static ssize_t tiers_store(struct kobject *kobj, goto restore; break; case '-': - ret =3D swap_tiers_remove(token + 1); + ret =3D swap_tiers_remove(token + 1, &mask); if (ret) goto restore; break; @@ -1053,7 +1054,7 @@ static ssize_t tiers_store(struct kobject *kobj, } } =20 - if (!swap_tiers_update()) { + if (!swap_tiers_update(mask)) { ret =3D -EINVAL; goto restore; } diff --git a/mm/swap_tier.c b/mm/swap_tier.c index 6b57cadb3e95..9c180f55a4e9 100644 --- a/mm/swap_tier.c +++ b/mm/swap_tier.c @@ -253,7 +253,7 @@ int swap_tiers_add(const char *name, int prio) return ret; } =20 -int swap_tiers_remove(const char *name) +int swap_tiers_remove(const char *name, int *mask) { int ret =3D 0; struct swap_tier *tier; @@ -276,6 +276,7 @@ int swap_tiers_remove(const char *name) list_prev_entry(tier, list)->prio =3D DEF_SWAP_PRIO; =20 swap_tier_inactivate(tier); + *mask |=3D TIER_MASK(tier); =20 return ret; } @@ -344,7 +345,26 @@ void swap_tiers_assign_dev(struct swap_info_struct *sw= p) swp->tier_mask =3D TIER_DEFAULT_MASK; } =20 -bool swap_tiers_update(void) +#ifdef CONFIG_MEMCG +static void swap_tier_memcg_propagate(int mask) +{ + struct mem_cgroup *child; + + rcu_read_lock(); + for_each_mem_cgroup_tree(child, root_mem_cgroup) { + WRITE_ONCE(child->tier_mask, child->tier_mask | mask); + WRITE_ONCE(child->tier_effective_mask, + child->tier_effective_mask | mask); + } + rcu_read_unlock(); +} +#else +static void swap_tier_memcg_propagate(int mask) +{ +} +#endif + +bool swap_tiers_update(int mask) { struct swap_tier *tier; struct swap_info_struct *swp; @@ -375,5 +395,88 @@ bool swap_tiers_update(void) swap_tiers_assign_dev(swp); } =20 + /* + * When a tier is removed, its index (bit position in the mask) becomes + * free for reassignment to a future tier. If a memcg had previously + * disabled this tier (cleared the bit in its swap.tiers file), the + * effective mask would keep that bit clear -- meaning the new tier at + * the same index would be silently unavailable, an invisible cgroup + * constraint left behind by a tier that no longer exists. + * + * To prevent this, OR the removed tier's mask bit into every memcg's + * tier_mask and tier_effective_mask. This resets the bit so the new + * tier is accessible by default; users who want to restrict it must + * explicitly disable it after the tier is re-created. + */ + if (mask) + swap_tier_memcg_propagate(mask); + return true; } + +#ifdef CONFIG_MEMCG +void swap_tiers_mask_show(struct seq_file *m, int mask) +{ + struct swap_tier *tier; + + spin_lock(&swap_tier_lock); + for_each_active_tier(tier) { + if (mask & TIER_MASK(tier)) + seq_printf(m, "%s ", tier->name); + } + spin_unlock(&swap_tier_lock); + seq_puts(m, "\n"); +} + +int swap_tiers_mask_lookup(const char *name) +{ + struct swap_tier *tier; + + lockdep_assert_held(&swap_tier_lock); + + for_each_active_tier(tier) { + if (!strcmp(name, tier->name)) + return TIER_MASK(tier); + } + + return 0; +} + +static void __swap_tier_memcg_inherit_mask(struct mem_cgroup *memcg, + struct mem_cgroup *parent) +{ + int parent_mask =3D parent + ? READ_ONCE(parent->tier_effective_mask) + : TIER_ALL_MASK; + + WRITE_ONCE(memcg->tier_effective_mask, + parent_mask & READ_ONCE(memcg->tier_mask)); +} + +/* Computes the initial effective mask from the parent's effective mask. */ +void swap_tiers_memcg_inherit_mask(struct mem_cgroup *memcg) +{ + spin_lock(&swap_tier_lock); + rcu_read_lock(); + memcg->tier_mask =3D TIER_ALL_MASK; + __swap_tier_memcg_inherit_mask(memcg, parent_mem_cgroup(memcg)); + rcu_read_unlock(); + spin_unlock(&swap_tier_lock); +} + +/* + * Called when a memcg's tier_mask is modified. Walks the subtree + * and recomputes each descendant's effective mask against its parent. + */ +void swap_tiers_memcg_sync_mask(struct mem_cgroup *memcg) +{ + struct mem_cgroup *child; + + lockdep_assert_held(&swap_tier_lock); + + rcu_read_lock(); + for_each_mem_cgroup_tree(child, memcg) + __swap_tier_memcg_inherit_mask(child, parent_mem_cgroup(child)); + rcu_read_unlock(); +} +#endif diff --git a/mm/swap_tier.h b/mm/swap_tier.h index 3e355f857363..49433dcaa1ce 100644 --- a/mm/swap_tier.h +++ b/mm/swap_tier.h @@ -10,22 +10,66 @@ struct swap_info_struct; =20 extern spinlock_t swap_tier_lock; =20 -#define TIER_ALL_MASK (~0) -#define TIER_DEFAULT_IDX (31) -#define TIER_DEFAULT_MASK (1U << TIER_DEFAULT_IDX) - /* Initialization and application */ void swap_tiers_init(void); ssize_t swap_tiers_sysfs_show(char *buf); =20 int swap_tiers_add(const char *name, int prio); -int swap_tiers_remove(const char *name); +int swap_tiers_remove(const char *name, int *mask); =20 void swap_tiers_snapshot(void); void swap_tiers_snapshot_restore(void); -bool swap_tiers_update(void); +bool swap_tiers_update(int mask); =20 /* Tier assignment */ void swap_tiers_assign_dev(struct swap_info_struct *swp); =20 +#define TIER_ALL_MASK (~0) +#define TIER_DEFAULT_IDX (31) +#define TIER_DEFAULT_MASK (1U << TIER_DEFAULT_IDX) + +#if defined(CONFIG_SWAP) && defined(CONFIG_MEMCG) +/* Memcg related functions */ +void swap_tiers_mask_show(struct seq_file *m, int mask); +void swap_tiers_memcg_inherit_mask(struct mem_cgroup *memcg); +void swap_tiers_memcg_sync_mask(struct mem_cgroup *memcg); +int swap_tiers_mask_lookup(const char *name); +static inline int folio_tier_effective_mask(struct folio *folio) +{ + struct mem_cgroup *memcg; + int mask =3D TIER_ALL_MASK; + + rcu_read_lock(); + memcg =3D folio_memcg(folio); + if (memcg) + mask =3D READ_ONCE(memcg->tier_effective_mask); + rcu_read_unlock(); + + return mask; +} +#else +static inline void swap_tiers_mask_show(struct seq_file *m, int mask) {} +static inline void swap_tiers_memcg_inherit_mask(struct mem_cgroup *memcg)= {} +static inline void swap_tiers_memcg_sync_mask(struct mem_cgroup *memcg) {} +static inline int swap_tiers_mask_lookup(const char *name) +{ + return 0; +} +static inline int folio_tier_effective_mask(struct folio *folio) +{ + return TIER_ALL_MASK; +} +#endif + +/** + * swap_tiers_mask_test - Check if the tier mask is valid + * @tier_mask: The tier mask to check + * @mask: The mask to compare against + * + * Return: true if condition matches, false otherwise + */ +static inline bool swap_tiers_mask_test(int tier_mask, int mask) +{ + return tier_mask & mask; +} #endif /* _SWAP_TIER_H */ --=20 2.34.1 From nobody Mon Jun 8 19:36:44 2026 Received: from lgeamrelo07.lge.com (lgeamrelo07.lge.com [156.147.51.103]) (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 D95C63161A2 for ; Wed, 27 May 2026 06:23:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=156.147.51.103 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779863034; cv=none; b=FUnULoQBzju/yg9C585zFeHkpa6v4mrwRu71uP2+n2PvhswLgTAb3Zq1/L+QKZ4A5RFYsqgFlgSLZCT0iF1MgTqHykLLHMzkjVbJ9ZPp8vHqj9aQ0BqOq8jtgD307jUplQeCWQUOfKaQES0N/YWxOEiOIjCBLXmcoYfD0MdsbX0= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779863034; c=relaxed/simple; bh=oay6c+jrn56hkFby6pQILUHzTTGLnQOfn55wjDbY36M=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=DFPVAk884qkxQJfwCs43rh16FPFO/jarYHzIFQZjHLtoYzbL8c4h2kmNEdF2NDTbKekzhmXlfUeQpBo5Sk54B/V3fFqC6jgNbvUFv+Ipg4xoYtVr6vlcEeTWeAEOSH9FPdRdYHgK1wZGd227cAbzxORS5Uo4pU/+WvL30tKoj9o= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=lge.com; spf=pass smtp.mailfrom=lge.com; arc=none smtp.client-ip=156.147.51.103 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=lge.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=lge.com Received: from unknown (HELO yjaykim-PowerEdge-T330.lge.net) (10.177.112.156) by 156.147.51.103 with ESMTP; 27 May 2026 15:23:50 +0900 X-Original-SENDERIP: 10.177.112.156 X-Original-MAILFROM: youngjun.park@lge.com From: Youngjun Park To: akpm@linux-foundation.org Cc: chrisl@kernel.org, youngjun.park@lge.com, linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kasong@tencent.com, hannes@cmpxchg.org, mhocko@kernel.org, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, shikemeng@huaweicloud.com, nphamcs@gmail.com, baoquan.he@linux.dev, baohua@kernel.org, gunho.lee@lge.com, taejoon.song@lge.com, hyungjun.cho@lge.com, mkoutny@suse.com, baver.bae@lge.com, matia.kim@lge.com Subject: [PATCH v7 4/4] mm: swap: filter swap allocation by memcg tier mask Date: Wed, 27 May 2026 15:22:47 +0900 Message-Id: <20260527062247.3440692-5-youngjun.park@lge.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260527062247.3440692-1-youngjun.park@lge.com> References: <20260527062247.3440692-1-youngjun.park@lge.com> 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" Apply memcg tier effective mask during swap slot allocation to enforce per-cgroup swap tier restrictions. In the fast path, check the percpu cached swap_info's tier_mask against the folio's effective mask. If it does not match, fall through to the slow path. In the slow path, skip swap devices whose tier_mask is not covered by the folio's effective mask. This works correctly when there is only one non-rotational device in the system and no devices share the same priority. However, there are known limitations: - When non-rotational devices are distributed across multiple tiers, and different memcgs are configured to use those distinct tiers, they may constantly overwrite the shared percpu swap cache. This cache thrashing leads to frequent fast path misses. - Combined with the above issue, if same-priority devices exist among them, a percpu cache miss (overwritten by another memcg) forces the allocator to round-robin to the next device prematurely, even if the current cluster is not fully exhausted. These edge cases do not affect the primary use case of directing swap traffic per cgroup. Further optimization is planned for future work. Signed-off-by: Youngjun Park Reviewed-by: Baoquan He Reviewed-by: Kairui Song Reviewed-by: Nhat Pham --- mm/swapfile.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/mm/swapfile.c b/mm/swapfile.c index 9a86ebe992f4..1a2d29735b71 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -1365,14 +1365,18 @@ static bool swap_alloc_fast(struct folio *folio) struct swap_cluster_info *ci; struct swap_info_struct *si; unsigned int offset; + int mask =3D folio_tier_effective_mask(folio); =20 /* * Once allocated, swap_info_struct will never be completely freed, * so checking it's liveness by get_swap_device_info is enough. */ si =3D this_cpu_read(percpu_swap_cluster.si[order]); + if (!si || !swap_tiers_mask_test(si->tier_mask, mask)) + return false; + offset =3D this_cpu_read(percpu_swap_cluster.offset[order]); - if (!si || !offset || !get_swap_device_info(si)) + if (!offset || !get_swap_device_info(si)) return false; =20 ci =3D swap_cluster_lock(si, offset); @@ -1392,10 +1396,14 @@ static bool swap_alloc_fast(struct folio *folio) static void swap_alloc_slow(struct folio *folio) { struct swap_info_struct *si, *next; + int mask =3D folio_tier_effective_mask(folio); =20 spin_lock(&swap_avail_lock); start_over: plist_for_each_entry_safe(si, next, &swap_avail_head, avail_list) { + if (!swap_tiers_mask_test(si->tier_mask, mask)) + continue; + /* Rotate the device and switch to a new cluster */ plist_requeue(&si->avail_list, &swap_avail_head); spin_unlock(&swap_avail_lock); --=20 2.34.1