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Thu, 17 Jul 2025 00:25:01 -0700 (PDT) X-Google-Smtp-Source: AGHT+IHKeRD3xCAGWa+dzntrbPMbsWyFZut7J2kc0oL6u2GZt3zXbRx6x0p+nqxW/PS1DVmbc3Wz61TqafQnGiZLg5E= X-Received: by 2002:a05:690c:1c:b0:70d:f237:6a6a with SMTP id 00721157ae682-71834fd3745mr68332027b3.11.1752737100915; Thu, 17 Jul 2025 00:25:00 -0700 (PDT) MIME-Version: 1.0 References: <20250714003207.113275-1-npache@redhat.com> <20250714003207.113275-7-npache@redhat.com> In-Reply-To: From: Nico Pache Date: Thu, 17 Jul 2025 01:24:34 -0600 X-Gm-Features: Ac12FXxyfnb4_RV9eEcRUqSxUtI2u4uwq8rBJNr3J875h2as7uY9eFcbia4dCv8 Message-ID: Subject: Re: [PATCH v9 06/14] khugepaged: introduce collapse_scan_bitmap for mTHP support To: "Liam R. Howlett" , Nico Pache , linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, david@redhat.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, lorenzo.stoakes@oracle.com, ryan.roberts@arm.com, dev.jain@arm.com, corbet@lwn.net, rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, akpm@linux-foundation.org, baohua@kernel.org, willy@infradead.org, peterx@redhat.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, 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, rdunlap@infradead.org, hughd@google.com X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: dkaWmLsXovF0p3lFtSIyQY1Se93ccEq8XW0w3VgmYLo_1752737102 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 45118C0009 X-Rspam-User: X-Rspamd-Server: rspam09 X-Stat-Signature: 85ey5y3r7wwukk3ugeyoyx9i1a81qrw5 X-HE-Tag: 1752737104-337625 X-HE-Meta: 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 Dmwm1Zrl AhVHop8YJ7nYiW8I92BP3QDemK77YByuZN9iQNN+nmM3k03nJnASq5UJwMCYwnK4Ip0qfPJSrYZR8MhluT8oqYzz7Js7Oll0CNNI4d0pXTi7a0XCfFtbiqGPycjmB3I432YnUsQ+IXjVLEWEtokiik9eBTcSDHkquq216cGxTkUxuvXpBi4ZpAg1uFe6u2yV9PAwKpgPSF2Sipug2C7ldXHkUzVaFxFV9+0qxoactMCslhyWoT8/nVlb/GiZlXpwy+o4QMsc7aEKcjDNpBYhv3Gi+bCWJQgjVLFhbWA+FPWt/Lt+kpHSQRinJ6Ww4pTZcG+EhHvFEJ6jMbhIEf2BY+fwwRx5zoO6OwHgbhhq4pZd0roPvK/DsgFQ2Wehs3wwIYKXYels3Zsncoos5FgUqkehsh/Q1TgHKuUEB6jVvx9XmW/I0I14Nsx2nR8MxktMo5wd1TKpkEkv+gFQ= 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 Wed, Jul 16, 2025 at 9:39=E2=80=AFAM Liam R. Howlett wrote: > > * Nico Pache [250713 20:34]: > > khugepaged scans anons PMD ranges for potential collapse to a hugepage. > > To add mTHP support we use this scan to instead record chunks of utiliz= ed > > sections of the PMD. > > > > collapse_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 whil= e > > scanning the anon PMD. A minimum collapse order of 2 is used as this is > > the lowest order supported by anon memory. > > > > max_ptes_none is used as a scale to determine how "full" an order must > > be before being considered for collapse. > > > > When attempting to collapse an order that has its order set to "always" > > lets always collapse to that order in a greedy manner without > > considering the number of bits set. > > > > v7 had talks about having selftests of this code. You mention you used > selftests mm in the cover letter but it seems you did not add the > reproducer that Baolin had? This was in relation to the MADV_COLLAPSE issue, which we decided to put off for now. I can add mTHP tests to my list of future work! -- Nico > > Maybe I missed that? > > > 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 ff6120463745..0f957711a117 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 2 > > +#define KHUGEPAGED_MIN_MTHP_NR (1< > +#define MAX_MTHP_BITMAP_SIZE (1 << (ilog2(MAX_PTRS_PER_PTE) - KHUGEPA= GED_MIN_MTHP_ORDER)) > > +#define MTHP_BITMAP_SIZE (1 << (HPAGE_PMD_ORDER - KHUGEPAGED_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 ee54e3c1db4e..59b2431ca616 100644 > > --- a/mm/khugepaged.c > > +++ b/mm/khugepaged.c > > @@ -94,6 +94,11 @@ static DEFINE_READ_MOSTLY_HASHTABLE(mm_slots_hash, M= M_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, > > }; > > > > /** > > @@ -838,10 +855,6 @@ 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 collapse_scan_abort(int nid, struct collapse_control *cc) > > { > > int i; > > @@ -1115,7 +1128,8 @@ static int alloc_charge_folio(struct folio **foli= op, struct mm_struct *mm, > > > > static int collapse_huge_page(struct mm_struct *mm, unsigned long addr= ess, > > 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; > > @@ -1134,8 +1148,12 @@ 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) > > @@ -1272,12 +1290,72 @@ static int collapse_huge_page(struct mm_struct = *mm, 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 collapse_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 collapse_scan_pmd(struct mm_struct *mm, > > struct vm_area_struct *vma, > > unsigned long address, bool *mmap_lock= ed, > > @@ -1444,9 +1522,7 @@ static int collapse_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, writable, referenced, > > -- > > 2.50.0 > > >