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Mon, 14 Apr 2025 16:07:21 -0700 (PDT) MIME-Version: 1.0 References: <20250414220557.35388-1-npache@redhat.com> <20250414220557.35388-7-npache@redhat.com> In-Reply-To: <20250414220557.35388-7-npache@redhat.com> From: Nico Pache Date: Mon, 14 Apr 2025 17:06:55 -0600 X-Gm-Features: ATxdqUH4QUCNJG6cSyqRQldW0r1-zIVuLoCx1f8277YmMIgHsCkj4qzTqmin7Mc Message-ID: Subject: Re: [PATCH v3 06/12] khugepaged: introduce khugepaged_scan_bitmap for mTHP support To: linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Cc: akpm@linux-foundation.org, corbet@lwn.net, rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, david@redhat.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, ryan.roberts@arm.com, willy@infradead.org, peterx@redhat.com, ziy@nvidia.com, wangkefeng.wang@huawei.com, usamaarif642@gmail.com, sunnanyong@huawei.com, vishal.moola@gmail.com, thomas.hellstrom@linux.intel.com, yang@os.amperecomputing.com, kirill.shutemov@linux.intel.com, aarcange@redhat.com, raquini@redhat.com, dev.jain@arm.com, anshuman.khandual@arm.com, catalin.marinas@arm.com, tiwai@suse.de, will@kernel.org, dave.hansen@linux.intel.com, jack@suse.cz, cl@gentwo.org, jglisse@google.com, surenb@google.com, zokeefe@google.com, hannes@cmpxchg.org, rientjes@google.com, mhocko@suse.com X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: anM4AecrlGerN00fgqzimTaug7WocuiXDDNO9ufofzA_1744672042 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: ECC551C0010 X-Stat-Signature: 87s4naxwdetd1xkebey6srx9szq4wjrf X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1744672044-977758 X-HE-Meta: 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 UFwPVbUe qrweOvEOkTiPmOgo9JkLZd6DCW3SXuWWW0KGA/TKi/6C7tpSA2Q2UKk/sk/h1Gn/x6Fbjyb9uvUMCSDU= 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: List-Subscribe: List-Unsubscribe: On Mon, Apr 14, 2025 at 4:07=E2=80=AFPM Nico Pache wrot= e: > > 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 MIN_MTHP_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 | 94 ++++++++++++++++++++++++++++++++++---- > 2 files changed, 89 insertions(+), 9 deletions(-) > > diff --git a/include/linux/khugepaged.h b/include/linux/khugepaged.h > index 1f46046080f5..60d41215bc1a 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 KHUGEPAGED_MIN_MTHP_ORDER 3 Somehow managed to drop #define KHUGEPAGED_MIN_MTHP_ORDER 2 When cleaning up my patches. Sending a V4 of just this patch in reply to this email. Sorry for the noise... > +#define KHUGEPAGED_MIN_MTHP_NR (1< +#define MAX_MTHP_BITMAP_SIZE (1 << (ilog2(MAX_PTRS_PER_PTE) - KHUGEPAGE= D_MIN_MTHP_ORDER)) > +#define MTHP_BITMAP_SIZE (1 << (HPAGE_PMD_ORDER - KHUGEPAGED_MIN_MTHP_O= RDER)) > > extern unsigned int khugepaged_max_ptes_none __read_mostly; > #ifdef CONFIG_TRANSPARENT_HUGEPAGE > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index dfecedc6a515..5a3be30096fc 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 +107,18 @@ struct collapse_control { > > /* nodemask for allocation fallback */ > nodemask_t alloc_nmask; > + > + /* > + * bitmap used to collapse mTHP sizes. > + * 1bit =3D order KHUGEPAGED_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 =3D { > + .is_khugepaged =3D true, > }; > > /** > @@ -851,10 +868,6 @@ static void khugepaged_alloc_sleep(void) > remove_wait_queue(&khugepaged_wait, &wait); > } > > -struct collapse_control khugepaged_collapse_control =3D { > - .is_khugepaged =3D true, > -}; > - > static bool khugepaged_scan_abort(int nid, struct collapse_control *cc) > { > int i; > @@ -1118,7 +1131,8 @@ static int alloc_charge_folio(struct folio **foliop= , struct mm_struct *mm, > > static int collapse_huge_page(struct mm_struct *mm, unsigned long addres= s, > int referenced, int unmapped, > - struct collapse_control *cc) > + struct collapse_control *cc, bool *mmap_loc= ked, > + u8 order, u16 offset) > { > LIST_HEAD(compound_pagelist); > pmd_t *pmd, _pmd; > @@ -1137,8 +1151,12 @@ 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 duri= ng > * that. We will recheck the vma after taking it again in write m= ode. > + * If collapsing mTHPs we may have already released the read_lock= . > */ > - mmap_read_unlock(mm); > + if (*mmap_locked) { > + mmap_read_unlock(mm); > + *mmap_locked =3D false; > + } > > result =3D alloc_charge_folio(&folio, mm, cc, HPAGE_PMD_ORDER); > if (result !=3D SCAN_SUCCEED) > @@ -1273,12 +1291,72 @@ static int collapse_huge_page(struct mm_struct *m= m, unsigned long address, > out_up_write: > mmap_write_unlock(mm); > out_nolock: > + *mmap_locked =3D false; > if (folio) > folio_put(folio); > trace_mm_collapse_huge_page(mm, result =3D=3D SCAN_SUCCEED, resul= t); > return result; > } > > +// Recursive function to consume the bitmap > +static int khugepaged_scan_bitmap(struct mm_struct *mm, unsigned long ad= dress, > + int referenced, int unmapped, struct collapse_con= trol *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 =3D -1; > + int collapsed =3D 0; > + int ret; > + struct scan_bit_state state; > + bool is_pmd_only =3D (enabled_orders =3D=3D (1 << HPAGE_PMD_ORDER= )); > + > + cc->mthp_bitmap_stack[++top] =3D (struct scan_bit_state) > + { HPAGE_PMD_ORDER - KHUGEPAGED_MIN_MTHP_ORDER, 0 }; > + > + while (top >=3D 0) { > + state =3D cc->mthp_bitmap_stack[top--]; > + order =3D state.order + KHUGEPAGED_MIN_MTHP_ORDER; > + offset =3D state.offset; > + num_chunks =3D 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 =3D bitmap_weight(cc->mthp_bitmap_temp, num_chun= ks); > + threshold_bits =3D (HPAGE_PMD_NR - khugepaged_max_ptes_no= ne - 1) > + >> (HPAGE_PMD_ORDER - state.order); > + > + //Check if the region is "almost full" based on the thres= hold > + if (bits_set > threshold_bits || is_pmd_only > + || test_bit(order, &huge_anon_orders_always)) { > + ret =3D collapse_huge_page(mm, address, reference= d, unmapped, cc, > + mmap_locked, order, offset * KHUG= EPAGED_MIN_MTHP_NR); > + if (ret =3D=3D SCAN_SUCCEED) { > + collapsed +=3D (1 << order); > + continue; > + } > + } > + > +next: > + if (state.order > 0) { > + next_order =3D state.order - 1; > + mid_offset =3D offset + (num_chunks / 2); > + cc->mthp_bitmap_stack[++top] =3D (struct scan_bit= _state) > + { next_order, mid_offset }; > + cc->mthp_bitmap_stack[++top] =3D (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_lock= ed, > @@ -1445,9 +1523,7 @@ static int khugepaged_scan_pmd(struct mm_struct *mm= , > pte_unmap_unlock(pte, ptl); > if (result =3D=3D SCAN_SUCCEED) { > result =3D collapse_huge_page(mm, address, referenced, > - unmapped, cc); > - /* collapse_huge_page will return with the mmap_lock rele= ased */ > - *mmap_locked =3D false; > + unmapped, cc, mmap_locked, HP= AGE_PMD_ORDER, 0); > } > out: > trace_mm_khugepaged_scan_pmd(mm, &folio->page, writable, referenc= ed, > -- > 2.48.1 >