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Howlett" , Nico Pache , David Hildenbrand , Ryan Roberts , Barry Song , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Wei Yang , Lorenzo Stoakes , Andrew Morton References: <20260118192253.9263-4-shivankg@amd.com> <20260118192253.9263-8-shivankg@amd.com> <829b62c8-e3eb-485f-8d7b-01419c841cc8@arm.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang In-Reply-To: <829b62c8-e3eb-485f-8d7b-01419c841cc8@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam12 X-Stat-Signature: eziekyephpxiixwcwenetud87c4ffuyq X-Rspamd-Queue-Id: 3A7DC40003 X-Rspam-User: X-HE-Tag: 1769071485-282002 X-HE-Meta: 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 qj2HACxN A6JRQosScMuGegEc3XpZ0oPkNe3nY3G8Y8/brGq2cOwT3hDZhizCSMnw/5N/TshbfEjZJkfi1n+3V6PeFbYk/pMEooQW20urUix1xuuU0qkfPP3+HT4tdOFbbKf1TiVf2Mu5JfXkqNN/A+wNVNGvfPrw9YZIlrLmg8x7cyPsf3qd3LTbEeUHlIMb1fRTMIMC4rmEXb6KSFBoo/iQUi8X4BVTVM1qzphURLEEFCu+SZjR48J1aOHSk9FTqVcBlih8NNpKc9q5a5AfOB7GKhA6x11WebuOKzl2wttbBSNKYWrGxDfBRg4PpcvQTYQ== 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 2026/1/22 15:32, Dev Jain wrote: > > On 19/01/26 12:52 am, Shivank Garg wrote: >> The khugepaged_scan_mm_slot() uses a 'progress' counter to limit the >> amount of work performed and consists of three components: >> 1. Transitioning to a new mm (+1). >> 2. Skipping an unsuitable VMA (+1). >> 3. Scanning a PMD-sized range (+HPAGE_PMD_NR). >> >> Consider a 1MB VMA sitting between two 2MB alignment boundaries: >> >> vma1 vma2 vma3 >> +----------+------+----------+ >> |2M |1M |2M | >> +----------+------+----------+ >> ^ ^ >> start end >> ^ >> hstart,hend > > Won't such a VMA be skipped by thp_vma_allowable_order()? That internally > checks, apart from eligibility by sysfs, that the extent of the VMA can > map a hugepage. Ah, you're right! I was worrying about a case that doesn't actually happen. Thanks, Lance > >> >> In this case, for vma2: >> hstart = round_up(start, HPAGE_PMD_SIZE) -> Next 2MB alignment >> hend = round_down(end, HPAGE_PMD_SIZE) -> Prev 2MB alignment >> >> Currently, since `hend <= hstart`, VMAs that are too small or unaligned >> to contain a hugepage are skipped without incrementing 'progress'. >> A process containing a large number of such small VMAs will unfairly >> consume more CPU cycles before yielding compared to a process with >> fewer, larger, or aligned VMAs. >> >> Fix this by incrementing progress when the `hend <= hstart` condition >> is met. >> >> Additionally, change 'progress' type to `unsigned int` to match both >> the 'pages' type and the function return value. >> >> Suggested-by: Wei Yang >> Reviewed-by: Wei Yang >> Reviewed-by: Lance Yang >> Signed-off-by: Shivank Garg >> --- >> >> Incorporate comment feedback from Lance: >> https://lore.kernel.org/linux-mm/6b408736-978a-4d40-adfc-97819951c3a6@linux.dev >> >> mm/khugepaged.c | 5 +++-- >> 1 file changed, 3 insertions(+), 2 deletions(-) >> >> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >> index 984294a16861..93ce39915f4a 100644 >> --- a/mm/khugepaged.c >> +++ b/mm/khugepaged.c >> @@ -2403,7 +2403,7 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result, >> struct mm_slot *slot; >> struct mm_struct *mm; >> struct vm_area_struct *vma; >> - int progress = 0; >> + unsigned int progress = 0; >> >> VM_BUG_ON(!pages); >> lockdep_assert_held(&khugepaged_mm_lock); >> @@ -2447,7 +2447,8 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result, >> } >> hstart = round_up(vma->vm_start, HPAGE_PMD_SIZE); >> hend = round_down(vma->vm_end, HPAGE_PMD_SIZE); >> - if (khugepaged_scan.address > hend) { >> + if (khugepaged_scan.address > hend || hend <= hstart) { >> + /* VMA already scanned or too small/unaligned for hugepage. */ >> progress++; >> continue; >> }