From patchwork Wed Jul 6 23:59:27 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Zach O'Keefe X-Patchwork-Id: 12908933 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 23342CCA480 for ; Thu, 7 Jul 2022 00:06:23 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 99A6A8E0009; Wed, 6 Jul 2022 20:06:22 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 9233B8E0001; Wed, 6 Jul 2022 20:06:22 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 7272E8E0009; Wed, 6 Jul 2022 20:06:22 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 54C478E0001 for ; Wed, 6 Jul 2022 20:06:22 -0400 (EDT) Received: from smtpin10.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 2905B206AC for ; Thu, 7 Jul 2022 00:06:22 +0000 (UTC) X-FDA: 79658361804.10.9761EB0 Received: from mail-pf1-f201.google.com (mail-pf1-f201.google.com [209.85.210.201]) by imf24.hostedemail.com (Postfix) with ESMTP id BCED718003F for ; Thu, 7 Jul 2022 00:06:21 +0000 (UTC) Received: by mail-pf1-f201.google.com with SMTP id d7-20020a056a0010c700b0052894ee16d8so2482649pfu.6 for ; Wed, 06 Jul 2022 17:06:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=FbSIKNrXiTKXBZpf/osMvXcfezTwMiY3lbG4Do0xf6Y=; b=eKwDk5+FZlVnb4XO0EqqWKl0a5+ipEJU7fLV7wkhHLuH9XjyqOCS3QO3qE7q+GQ8kO azh3sHGngdfbftASUQ45C4FTpQ+ZY3c2cbfVdPRkoCL5tKhB4DbUx8B0YXl/pg0UaSG8 wHOKnxbEggPlJ5cmd9UhWNgFXqHCBsq4HWR+iVrPZqncaabu6mjYJBPlLChhQrcAjf3/ /bJxi07q5uBIZxaag0UsFynie71hkppVU/T8wiseX85GzRSPfKQYIon5uGU7UN+nqFRy esY8ZIS6p4N53OgEjfv36c/3WQVCkx4jvBVSqCq+n0yiCPz6extaB9Jye2SptELquTaJ nmgg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=FbSIKNrXiTKXBZpf/osMvXcfezTwMiY3lbG4Do0xf6Y=; b=X3konK791Pm5tGuF15a6iDTrM9Rv/y3F6XEHidILBSJNdf0L9eXReIJegTVpprWR8l OeBb7F/ME4Orrh065cY3UBTehwMNxU9hB18Szgg6StHsCcVUiepo+o61wu4lyskVZbjJ qrqGlIBNsPr6AKDvtOzfDthti1sKa6D8ReYf7GENEQ3nEus4LKeIUGpgZKuRxSNWIc6s cdGVUsK4nOki+J6LGjNe64y+KAYvNF3Yv5jbbAzPVdUZcX6SKfp6LcQxUupsD2EdokWh gp64gFd63UjgW37GKV2POLMBxe/8ZM8inOgPe7prZ6NFns8glg8hlq1dCh816HMcEMQw fpZg== X-Gm-Message-State: AJIora+S+0x7wLrAkFJaip3TBcv1TURUluJsywLVfk0cvt+iQCSdacfy ybbRXTLeEhc9zoYgcy9bsgOA25U5ZdKB X-Google-Smtp-Source: AGRyM1uR4TMMkmWUsZBt1XuBJEJ6q0cNl0OGYwFe/ZgQPByN226hj8D5ikZ37JJuNAt6QZkALxmxKgq2sSAK X-Received: from zokeefe3.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:1b6]) (user=zokeefe job=sendgmr) by 2002:a17:90a:249:b0:1e0:a8a3:3c6c with SMTP id t9-20020a17090a024900b001e0a8a33c6cmr17113pje.0.1657152380188; Wed, 06 Jul 2022 17:06:20 -0700 (PDT) Date: Wed, 6 Jul 2022 16:59:27 -0700 In-Reply-To: <20220706235936.2197195-1-zokeefe@google.com> Message-Id: <20220706235936.2197195-10-zokeefe@google.com> Mime-Version: 1.0 References: <20220706235936.2197195-1-zokeefe@google.com> X-Mailer: git-send-email 2.37.0.rc0.161.g10f37bed90-goog Subject: [mm-unstable v7 09/18] mm/madvise: introduce MADV_COLLAPSE sync hugepage collapse From: "Zach O'Keefe" To: Alex Shi , David Hildenbrand , David Rientjes , Matthew Wilcox , Michal Hocko , Pasha Tatashin , Peter Xu , Rongwei Wang , SeongJae Park , Song Liu , Vlastimil Babka , Yang Shi , Zi Yan , linux-mm@kvack.org Cc: Andrea Arcangeli , Andrew Morton , Arnd Bergmann , Axel Rasmussen , Chris Kennelly , Chris Zankel , Helge Deller , Hugh Dickins , Ivan Kokshaysky , "James E.J. Bottomley" , Jens Axboe , "Kirill A. Shutemov" , Matt Turner , Max Filippov , Miaohe Lin , Minchan Kim , Patrick Xia , Pavel Begunkov , Thomas Bogendoerfer , "Zach O'Keefe" ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1657152381; a=rsa-sha256; cv=none; b=ryo1tMO6yd+ZCyHWhO6kIcuo8Sbl/d9PUsfS2ReAdfumtWRT75/ir4hbdxSUnIj8my9ABi Pqs6yEhG5pqzZE+8x+mkbXU2zoJZHYii99iJjZHTm2plEXkxyoy8jPMDRbYL9YiJj6jecb cUSBQWe8aLyLJJ3y3pFQNtu9BeRO41w= ARC-Authentication-Results: i=1; imf24.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=eKwDk5+F; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf24.hostedemail.com: domain of 3fCPGYgcKCPcynjddedfnnfkd.bnlkhmtw-lljuZbj.nqf@flex--zokeefe.bounces.google.com designates 209.85.210.201 as permitted sender) smtp.mailfrom=3fCPGYgcKCPcynjddedfnnfkd.bnlkhmtw-lljuZbj.nqf@flex--zokeefe.bounces.google.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1657152381; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=FbSIKNrXiTKXBZpf/osMvXcfezTwMiY3lbG4Do0xf6Y=; b=vidFlU2elGTkaNYAKWdDmuMqzdmaUxfYboVxCPAmE5pFJT6bt+zm7UFNF84pphnnwyF0sO 40tYG6fDefR9wzxjd0JSd3s7WaSPt4J/YwlMp5TBZuTi1JelRKk7BrnViVwf9HQFn/ZkYs rXtKl4VvGnsX3yG8MhVRGLVy0+yVMDs= Authentication-Results: imf24.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=eKwDk5+F; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf24.hostedemail.com: domain of 3fCPGYgcKCPcynjddedfnnfkd.bnlkhmtw-lljuZbj.nqf@flex--zokeefe.bounces.google.com designates 209.85.210.201 as permitted sender) smtp.mailfrom=3fCPGYgcKCPcynjddedfnnfkd.bnlkhmtw-lljuZbj.nqf@flex--zokeefe.bounces.google.com X-Stat-Signature: giskg7rukjcgwesfhqftzmn4xpd9wfdz X-Rspamd-Queue-Id: BCED718003F X-Rspamd-Server: rspam05 X-Rspam-User: X-HE-Tag: 1657152381-761211 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: This idea was introduced by David Rientjes[1]. Introduce a new madvise mode, MADV_COLLAPSE, that allows users to request a synchronous collapse of memory at their own expense. The benefits of this approach are: * CPU is charged to the process that wants to spend the cycles for the THP * Avoid unpredictable timing of khugepaged collapse Semantics This call is independent of the system-wide THP sysfs settings, but will fail for memory marked VM_NOHUGEPAGE. If the ranges provided span multiple VMAs, the semantics of the collapse over each VMA is independent from the others. This implies a hugepage cannot cross a VMA boundary. If collapse of a given hugepage-aligned/sized region fails, the operation may continue to attempt collapsing the remainder of memory specified. The memory ranges provided must be page-aligned, but are not required to be hugepage-aligned. If the memory ranges are not hugepage-aligned, the start/end of the range will be clamped to the first/last hugepage-aligned address covered by said range. The memory ranges must span at least one hugepage-sized region. All non-resident pages covered by the range will first be swapped/faulted-in, before being internally copied onto a freshly allocated hugepage. Unmapped pages will have their data directly initialized to 0 in the new hugepage. However, for every eligible hugepage aligned/sized region to-be collapsed, at least one page must currently be backed by memory (a PMD covering the address range must already exist). Allocation for the new hugepage may enter direct reclaim and/or compaction, regardless of VMA flags. When the system has multiple NUMA nodes, the hugepage will be allocated from the node providing the most native pages. This operation operates on the current state of the specified process and makes no persistent changes or guarantees on how pages will be mapped, constructed, or faulted in the future Return Value If all hugepage-sized/aligned regions covered by the provided range were either successfully collapsed, or were already PMD-mapped THPs, this operation will be deemed successful. On success, process_madvise(2) returns the number of bytes advised, and madvise(2) returns 0. Else, -1 is returned and errno is set to indicate the error for the most-recently attempted hugepage collapse. Note that many failures might have occurred, since the operation may continue to collapse in the event a single hugepage-sized/aligned region fails. ENOMEM Memory allocation failed or VMA not found EBUSY Memcg charging failed EAGAIN Required resource temporarily unavailable. Try again might succeed. EINVAL Other error: No PMD found, subpage doesn't have Present bit set, "Special" page no backed by struct page, VMA incorrectly sized, address not page-aligned, ... Most notable here is ENOMEM and EBUSY (new to madvise) which are intended to provide the caller with actionable feedback so they may take an appropriate fallback measure. Use Cases An immediate user of this new functionality are malloc() implementations that manage memory in hugepage-sized chunks, but sometimes subrelease memory back to the system in native-sized chunks via MADV_DONTNEED; zapping the pmd. Later, when the memory is hot, the implementation could madvise(MADV_COLLAPSE) to re-back the memory by THPs to regain hugepage coverage and dTLB performance. TCMalloc is such an implementation that could benefit from this[2]. Only privately-mapped anon memory is supported for now, but additional support for file, shmem, and HugeTLB high-granularity mappings[2] is expected. File and tmpfs/shmem support would permit: * Backing executable text by THPs. Current support provided by CONFIG_READ_ONLY_THP_FOR_FS may take a long time on a large system which might impair services from serving at their full rated load after (re)starting. Tricks like mremap(2)'ing text onto anonymous memory to immediately realize iTLB performance prevents page sharing and demand paging, both of which increase steady state memory footprint. With MADV_COLLAPSE, we get the best of both worlds: Peak upfront performance and lower RAM footprints. * Backing guest memory by hugapages after the memory contents have been migrated in native-page-sized chunks to a new host, in a userfaultfd-based live-migration stack. [1] https://lore.kernel.org/linux-mm/d098c392-273a-36a4-1a29-59731cdf5d3d@google.com/ [2] https://github.com/google/tcmalloc/tree/master/tcmalloc Suggested-by: David Rientjes Signed-off-by: Zach O'Keefe Reviewed-by: Yang Shi --- arch/alpha/include/uapi/asm/mman.h | 2 + arch/mips/include/uapi/asm/mman.h | 2 + arch/parisc/include/uapi/asm/mman.h | 2 + arch/xtensa/include/uapi/asm/mman.h | 2 + include/linux/huge_mm.h | 14 ++- include/uapi/asm-generic/mman-common.h | 2 + mm/khugepaged.c | 118 ++++++++++++++++++- mm/madvise.c | 5 + tools/include/uapi/asm-generic/mman-common.h | 2 + 9 files changed, 146 insertions(+), 3 deletions(-) diff --git a/arch/alpha/include/uapi/asm/mman.h b/arch/alpha/include/uapi/asm/mman.h index 4aa996423b0d..763929e814e9 100644 --- a/arch/alpha/include/uapi/asm/mman.h +++ b/arch/alpha/include/uapi/asm/mman.h @@ -76,6 +76,8 @@ #define MADV_DONTNEED_LOCKED 24 /* like DONTNEED, but drop locked pages too */ +#define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */ + /* compatibility flags */ #define MAP_FILE 0 diff --git a/arch/mips/include/uapi/asm/mman.h b/arch/mips/include/uapi/asm/mman.h index 1be428663c10..c6e1fc77c996 100644 --- a/arch/mips/include/uapi/asm/mman.h +++ b/arch/mips/include/uapi/asm/mman.h @@ -103,6 +103,8 @@ #define MADV_DONTNEED_LOCKED 24 /* like DONTNEED, but drop locked pages too */ +#define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */ + /* compatibility flags */ #define MAP_FILE 0 diff --git a/arch/parisc/include/uapi/asm/mman.h b/arch/parisc/include/uapi/asm/mman.h index a7ea3204a5fa..22133a6a506e 100644 --- a/arch/parisc/include/uapi/asm/mman.h +++ b/arch/parisc/include/uapi/asm/mman.h @@ -70,6 +70,8 @@ #define MADV_WIPEONFORK 71 /* Zero memory on fork, child only */ #define MADV_KEEPONFORK 72 /* Undo MADV_WIPEONFORK */ +#define MADV_COLLAPSE 73 /* Synchronous hugepage collapse */ + #define MADV_HWPOISON 100 /* poison a page for testing */ #define MADV_SOFT_OFFLINE 101 /* soft offline page for testing */ diff --git a/arch/xtensa/include/uapi/asm/mman.h b/arch/xtensa/include/uapi/asm/mman.h index 7966a58af472..1ff0c858544f 100644 --- a/arch/xtensa/include/uapi/asm/mman.h +++ b/arch/xtensa/include/uapi/asm/mman.h @@ -111,6 +111,8 @@ #define MADV_DONTNEED_LOCKED 24 /* like DONTNEED, but drop locked pages too */ +#define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */ + /* compatibility flags */ #define MAP_FILE 0 diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h index 00312fc251c1..39193623442e 100644 --- a/include/linux/huge_mm.h +++ b/include/linux/huge_mm.h @@ -218,6 +218,9 @@ void __split_huge_pud(struct vm_area_struct *vma, pud_t *pud, int hugepage_madvise(struct vm_area_struct *vma, unsigned long *vm_flags, int advice); +int madvise_collapse(struct vm_area_struct *vma, + struct vm_area_struct **prev, + unsigned long start, unsigned long end); void vma_adjust_trans_huge(struct vm_area_struct *vma, unsigned long start, unsigned long end, long adjust_next); spinlock_t *__pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma); @@ -361,9 +364,16 @@ static inline void split_huge_pmd_address(struct vm_area_struct *vma, static inline int hugepage_madvise(struct vm_area_struct *vma, unsigned long *vm_flags, int advice) { - BUG(); - return 0; + return -EINVAL; } + +static inline int madvise_collapse(struct vm_area_struct *vma, + struct vm_area_struct **prev, + unsigned long start, unsigned long end) +{ + return -EINVAL; +} + static inline void vma_adjust_trans_huge(struct vm_area_struct *vma, unsigned long start, unsigned long end, diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h index 6c1aa92a92e4..6ce1f1ceb432 100644 --- a/include/uapi/asm-generic/mman-common.h +++ b/include/uapi/asm-generic/mman-common.h @@ -77,6 +77,8 @@ #define MADV_DONTNEED_LOCKED 24 /* like DONTNEED, but drop locked pages too */ +#define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */ + /* compatibility flags */ #define MAP_FILE 0 diff --git a/mm/khugepaged.c b/mm/khugepaged.c index c7a09cc9a0e8..2b2d832e44f2 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -976,7 +976,8 @@ static int alloc_charge_hpage(struct page **hpage, struct mm_struct *mm, struct collapse_control *cc) { /* Only allocate from the target node */ - gfp_t gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE; + gfp_t gfp = (cc->is_khugepaged ? alloc_hugepage_khugepaged_gfpmask() : + GFP_TRANSHUGE) | __GFP_THISNODE; int node = khugepaged_find_target_node(cc); if (!khugepaged_alloc_page(hpage, gfp, node)) @@ -2356,3 +2357,118 @@ void khugepaged_min_free_kbytes_update(void) set_recommended_min_free_kbytes(); mutex_unlock(&khugepaged_mutex); } + +static int madvise_collapse_errno(enum scan_result r) +{ + /* + * MADV_COLLAPSE breaks from existing madvise(2) conventions to provide + * actionable feedback to caller, so they may take an appropriate + * fallback measure depending on the nature of the failure. + */ + switch (r) { + case SCAN_ALLOC_HUGE_PAGE_FAIL: + return -ENOMEM; + case SCAN_CGROUP_CHARGE_FAIL: + return -EBUSY; + /* Resource temporary unavailable - trying again might succeed */ + case SCAN_PAGE_LOCK: + case SCAN_PAGE_LRU: + return -EAGAIN; + /* + * Other: Trying again likely not to succeed / error intrinsic to + * specified memory range. khugepaged likely won't be able to collapse + * either. + */ + default: + return -EINVAL; + } +} + +int madvise_collapse(struct vm_area_struct *vma, struct vm_area_struct **prev, + unsigned long start, unsigned long end) +{ + struct collapse_control *cc; + struct mm_struct *mm = vma->vm_mm; + unsigned long hstart, hend, addr; + int thps = 0, last_fail = SCAN_FAIL; + bool mmap_locked = true; + + BUG_ON(vma->vm_start > start); + BUG_ON(vma->vm_end < end); + + cc = kmalloc(sizeof(*cc), GFP_KERNEL); + if (!cc) + return -ENOMEM; + cc->is_khugepaged = false; + cc->last_target_node = NUMA_NO_NODE; + + *prev = vma; + + /* TODO: Support file/shmem */ + if (!vma->anon_vma || !vma_is_anonymous(vma)) + return -EINVAL; + + hstart = (start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK; + hend = end & HPAGE_PMD_MASK; + + if (!hugepage_vma_check(vma, vma->vm_flags, false, false, false)) + return -EINVAL; + + mmgrab(mm); + lru_add_drain_all(); + + for (addr = hstart; addr < hend; addr += HPAGE_PMD_SIZE) { + int result = SCAN_FAIL; + + if (!mmap_locked) { + cond_resched(); + mmap_read_lock(mm); + mmap_locked = true; + result = hugepage_vma_revalidate(mm, addr, &vma, cc); + if (result != SCAN_SUCCEED) { + last_fail = result; + goto out_nolock; + } + } + mmap_assert_locked(mm); + memset(cc->node_load, 0, sizeof(cc->node_load)); + result = khugepaged_scan_pmd(mm, vma, addr, &mmap_locked, cc); + if (!mmap_locked) + *prev = NULL; /* Tell caller we dropped mmap_lock */ + + switch (result) { + case SCAN_SUCCEED: + case SCAN_PMD_MAPPED: + ++thps; + break; + /* Whitelisted set of results where continuing OK */ + case SCAN_PMD_NULL: + case SCAN_PTE_NON_PRESENT: + case SCAN_PTE_UFFD_WP: + case SCAN_PAGE_RO: + case SCAN_LACK_REFERENCED_PAGE: + case SCAN_PAGE_NULL: + case SCAN_PAGE_COUNT: + case SCAN_PAGE_LOCK: + case SCAN_PAGE_COMPOUND: + case SCAN_PAGE_LRU: + last_fail = result; + break; + default: + last_fail = result; + /* Other error, exit */ + goto out_maybelock; + } + } + +out_maybelock: + /* Caller expects us to hold mmap_lock on return */ + if (!mmap_locked) + mmap_read_lock(mm); +out_nolock: + mmap_assert_locked(mm); + mmdrop(mm); + + return thps == ((hend - hstart) >> HPAGE_PMD_SHIFT) ? 0 + : madvise_collapse_errno(last_fail); +} diff --git a/mm/madvise.c b/mm/madvise.c index 851fa4e134bc..9f08e958ea86 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -59,6 +59,7 @@ static int madvise_need_mmap_write(int behavior) case MADV_FREE: case MADV_POPULATE_READ: case MADV_POPULATE_WRITE: + case MADV_COLLAPSE: return 0; default: /* be safe, default to 1. list exceptions explicitly */ @@ -1057,6 +1058,8 @@ static int madvise_vma_behavior(struct vm_area_struct *vma, if (error) goto out; break; + case MADV_COLLAPSE: + return madvise_collapse(vma, prev, start, end); } anon_name = anon_vma_name(vma); @@ -1150,6 +1153,7 @@ madvise_behavior_valid(int behavior) #ifdef CONFIG_TRANSPARENT_HUGEPAGE case MADV_HUGEPAGE: case MADV_NOHUGEPAGE: + case MADV_COLLAPSE: #endif case MADV_DONTDUMP: case MADV_DODUMP: @@ -1339,6 +1343,7 @@ int madvise_set_anon_name(struct mm_struct *mm, unsigned long start, * MADV_NOHUGEPAGE - mark the given range as not worth being backed by * transparent huge pages so the existing pages will not be * coalesced into THP and new pages will not be allocated as THP. + * MADV_COLLAPSE - synchronously coalesce pages into new THP. * MADV_DONTDUMP - the application wants to prevent pages in the given range * from being included in its core dump. * MADV_DODUMP - cancel MADV_DONTDUMP: no longer exclude from core dump. diff --git a/tools/include/uapi/asm-generic/mman-common.h b/tools/include/uapi/asm-generic/mman-common.h index 6c1aa92a92e4..6ce1f1ceb432 100644 --- a/tools/include/uapi/asm-generic/mman-common.h +++ b/tools/include/uapi/asm-generic/mman-common.h @@ -77,6 +77,8 @@ #define MADV_DONTNEED_LOCKED 24 /* like DONTNEED, but drop locked pages too */ +#define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */ + /* compatibility flags */ #define MAP_FILE 0