From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 4FDD219D8A0; Mon, 17 Feb 2025 07:27:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739777259; cv=none; b=WwUWjrMuc1EC/TAaYkojscIAiertN7UfzF0xij5lZP5kxNmbiyV7/DhuU6QYO3sBRrxIFs2PkhY0kdApF2JalllkgBILQh7YRH1knv3ii4OziCy7fpiDTw09rMfXZ626HODfWzm9ai6jvS/QxeQdDh7aOhC8SeV6JxtdUOx3zsQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739777259; c=relaxed/simple; bh=UeWwVPWbzIIAgtLdrtpQdDnl7IKv66IredifQ9C1934=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=fw65lCVq56SOQFBNSEjKWltpz8qG45BYepzFiLSk4UboINYamDnkGuUjopvZ/IVnAgEuDqNF2KRuK8plPk02G/OKQE1beyvCtghPUnhjDn42UuYc6uXT8G8V8PLRUAEuh3R1+DqLvEPMFCtlrZ+S3TrdsY2gRZM/Ko7DRCLshuU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id DD608FEC; Sun, 16 Feb 2025 23:27:55 -0800 (PST) Received: from [10.162.41.27] (K4MQJ0H1H2.blr.arm.com [10.162.41.27]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A61563F6A8; Sun, 16 Feb 2025 23:27:23 -0800 (PST) Message-ID: <021f76c6-f9d5-4685-814f-4d6c573b22e6@arm.com> Date: Mon, 17 Feb 2025 12:57:20 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC v2 6/9] khugepaged: introduce khugepaged_scan_bitmap for mTHP support To: Nico Pache , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-mm@kvack.org Cc: ryan.roberts@arm.com, anshuman.khandual@arm.com, catalin.marinas@arm.com, cl@gentwo.org, vbabka@suse.cz, mhocko@suse.com, apopple@nvidia.com, dave.hansen@linux.intel.com, will@kernel.org, baohua@kernel.org, jack@suse.cz, srivatsa@csail.mit.edu, haowenchao22@gmail.com, hughd@google.com, aneesh.kumar@kernel.org, yang@os.amperecomputing.com, peterx@redhat.com, ioworker0@gmail.com, wangkefeng.wang@huawei.com, ziy@nvidia.com, jglisse@google.com, surenb@google.com, vishal.moola@gmail.com, zokeefe@google.com, zhengqi.arch@bytedance.com, jhubbard@nvidia.com, 21cnbao@gmail.com, willy@infradead.org, kirill.shutemov@linux.intel.com, david@redhat.com, aarcange@redhat.com, raquini@redhat.com, sunnanyong@huawei.com, usamaarif642@gmail.com, audra@redhat.com, akpm@linux-foundation.org, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, tiwai@suse.de References: <20250211003028.213461-1-npache@redhat.com> <20250211003028.213461-7-npache@redhat.com> Content-Language: en-US From: Dev Jain In-Reply-To: <20250211003028.213461-7-npache@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 11/02/25 6:00 am, Nico Pache wrote: > khugepaged scans PMD ranges for potential collapse to a hugepage. To add > mTHP support we use this scan to instead record chunks of fully utilized > sections of the PMD. > > create a bitmap to represent a PMD in order MTHP_MIN_ORDER chunks. > by default we will set this to order 3. The reasoning is that for 4K 512 > PMD size this results in a 64 bit bitmap which has some optimizations. > For other arches like ARM64 64K, we can set a larger order if needed. > > khugepaged_scan_bitmap uses a stack struct to recursively scan a bitmap > that represents chunks of utilized regions. We can then determine what > mTHP size fits best and in the following patch, we set this bitmap while > scanning the PMD. > > max_ptes_none is used as a scale to determine how "full" an order must > be before being considered for collapse. > > If a order is set to "always" lets always collapse to that order in a > greedy manner. > > Signed-off-by: Nico Pache > --- > include/linux/khugepaged.h | 4 ++ > mm/khugepaged.c | 89 +++++++++++++++++++++++++++++++++++--- > 2 files changed, 86 insertions(+), 7 deletions(-) > > diff --git a/include/linux/khugepaged.h b/include/linux/khugepaged.h > index 1f46046080f5..1fe0c4fc9d37 100644 > --- a/include/linux/khugepaged.h > +++ b/include/linux/khugepaged.h > @@ -1,6 +1,10 @@ > /* SPDX-License-Identifier: GPL-2.0 */ > #ifndef _LINUX_KHUGEPAGED_H > #define _LINUX_KHUGEPAGED_H > +#define MIN_MTHP_ORDER 3 > +#define MIN_MTHP_NR (1< +#define MAX_MTHP_BITMAP_SIZE (1 << (ilog2(MAX_PTRS_PER_PTE * PAGE_SIZE) - MIN_MTHP_ORDER)) > +#define MTHP_BITMAP_SIZE (1 << (HPAGE_PMD_ORDER - MIN_MTHP_ORDER)) > > extern unsigned int khugepaged_max_ptes_none __read_mostly; > #ifdef CONFIG_TRANSPARENT_HUGEPAGE > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 3776055bd477..c8048d9ec7fb 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -94,6 +94,11 @@ static DEFINE_READ_MOSTLY_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS); > > static struct kmem_cache *mm_slot_cache __ro_after_init; > > +struct scan_bit_state { > + u8 order; > + u16 offset; > +}; > + > struct collapse_control { > bool is_khugepaged; > > @@ -102,6 +107,15 @@ struct collapse_control { > > /* nodemask for allocation fallback */ > nodemask_t alloc_nmask; > + > + /* bitmap used to collapse mTHP sizes. 1bit = order MIN_MTHP_ORDER mTHP */ > + DECLARE_BITMAP(mthp_bitmap, MAX_MTHP_BITMAP_SIZE); > + DECLARE_BITMAP(mthp_bitmap_temp, MAX_MTHP_BITMAP_SIZE); > + struct scan_bit_state mthp_bitmap_stack[MAX_MTHP_BITMAP_SIZE]; > +}; > + > +struct collapse_control khugepaged_collapse_control = { > + .is_khugepaged = true, > }; > > /** > @@ -851,10 +865,6 @@ static void khugepaged_alloc_sleep(void) > remove_wait_queue(&khugepaged_wait, &wait); > } > > -struct collapse_control khugepaged_collapse_control = { > - .is_khugepaged = true, > -}; > - > static bool khugepaged_scan_abort(int nid, struct collapse_control *cc) > { > int i; > @@ -1112,7 +1122,8 @@ static int alloc_charge_folio(struct folio **foliop, struct mm_struct *mm, > > static int collapse_huge_page(struct mm_struct *mm, unsigned long address, > int referenced, int unmapped, > - struct collapse_control *cc) > + struct collapse_control *cc, bool *mmap_locked, > + u8 order, u16 offset) > { > LIST_HEAD(compound_pagelist); > pmd_t *pmd, _pmd; > @@ -1130,8 +1141,12 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address, > * The allocation can take potentially a long time if it involves > * sync compaction, and we do not need to hold the mmap_lock during > * that. We will recheck the vma after taking it again in write mode. > + * If collapsing mTHPs we may have already released the read_lock. > */ > - mmap_read_unlock(mm); > + if (*mmap_locked) { > + mmap_read_unlock(mm); > + *mmap_locked = false; > + } > > result = alloc_charge_folio(&folio, mm, cc, HPAGE_PMD_ORDER); > if (result != SCAN_SUCCEED) > @@ -1266,12 +1281,71 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address, > out_up_write: > mmap_write_unlock(mm); > out_nolock: > + *mmap_locked = false; > if (folio) > folio_put(folio); > trace_mm_collapse_huge_page(mm, result == SCAN_SUCCEED, result); > return result; > } > > +// Recursive function to consume the bitmap > +static int khugepaged_scan_bitmap(struct mm_struct *mm, unsigned long address, > + int referenced, int unmapped, struct collapse_control *cc, > + bool *mmap_locked, unsigned long enabled_orders) > +{ > + u8 order, next_order; > + u16 offset, mid_offset; > + int num_chunks; > + int bits_set, threshold_bits; > + int top = -1; > + int collapsed = 0; > + int ret; > + struct scan_bit_state state; > + > + cc->mthp_bitmap_stack[++top] = (struct scan_bit_state) > + { HPAGE_PMD_ORDER - MIN_MTHP_ORDER, 0 }; > + > + while (top >= 0) { > + state = cc->mthp_bitmap_stack[top--]; > + order = state.order + MIN_MTHP_ORDER; > + offset = state.offset; > + num_chunks = 1 << (state.order); > + // Skip mTHP orders that are not enabled > + if (!test_bit(order, &enabled_orders)) > + goto next; > + > + // copy the relavant section to a new bitmap > + bitmap_shift_right(cc->mthp_bitmap_temp, cc->mthp_bitmap, offset, > + MTHP_BITMAP_SIZE); > + > + bits_set = bitmap_weight(cc->mthp_bitmap_temp, num_chunks); > + threshold_bits = (HPAGE_PMD_NR - khugepaged_max_ptes_none - 1) > + >> (HPAGE_PMD_ORDER - state.order); > + > + //Check if the region is "almost full" based on the threshold > + if (bits_set > threshold_bits > + || test_bit(order, &huge_anon_orders_always)) { > + ret = collapse_huge_page(mm, address, referenced, unmapped, cc, > + mmap_locked, order, offset * MIN_MTHP_NR); > + if (ret == SCAN_SUCCEED) { > + collapsed += (1 << order); > + continue; > + } If collapse_huge_page() fails due to hugepage_vma_revalidate() or find_pmd_or_thp_or_none(), you should exit. > + } > + > +next: > + if (state.order > 0) { > + next_order = state.order - 1; > + mid_offset = offset + (num_chunks / 2); > + cc->mthp_bitmap_stack[++top] = (struct scan_bit_state) > + { next_order, mid_offset }; > + cc->mthp_bitmap_stack[++top] = (struct scan_bit_state) > + { next_order, offset }; > + } > + } > + return collapsed; > +} > + > static int khugepaged_scan_pmd(struct mm_struct *mm, > struct vm_area_struct *vma, > unsigned long address, bool *mmap_locked, > @@ -1440,7 +1514,7 @@ static int khugepaged_scan_pmd(struct mm_struct *mm, > pte_unmap_unlock(pte, ptl); > if (result == SCAN_SUCCEED) { > result = collapse_huge_page(mm, address, referenced, > - unmapped, cc); > + unmapped, cc, mmap_locked, HPAGE_PMD_ORDER, 0); > /* collapse_huge_page will return with the mmap_lock released */ > *mmap_locked = false; > } > @@ -2856,6 +2930,7 @@ int madvise_collapse(struct vm_area_struct *vma, struct vm_area_struct **prev, > mmdrop(mm); > kfree(cc); > > + > return thps == ((hend - hstart) >> HPAGE_PMD_SHIFT) ? 0 > : madvise_collapse_errno(last_fail); > }