From: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
To: David Hildenbrand <david@redhat.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>,
Hugh Dickins <hughd@google.com>,
akpm@linux-foundation.org, ziy@nvidia.com,
Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com,
dev.jain@arm.com, baohua@kernel.org, zokeefe@google.com,
shy828301@gmail.com, usamaarif642@gmail.com, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 0/2] fix MADV_COLLAPSE issue if THP settings are disabled
Date: Wed, 25 Jun 2025 11:15:21 +0100 [thread overview]
Message-ID: <eb0c8d93-cd9f-4b57-a0f0-d30cdb5b31bc@lucifer.local> (raw)
In-Reply-To: <5de8ca8e-f293-4bfc-b49d-6e2a2e049f2b@redhat.com>
On Wed, Jun 25, 2025 at 12:07:12PM +0200, David Hildenbrand wrote:
> > Yes, I don't mean it will prevent madvise_collapse(), just as you said
> > that it could be problematic (it's horrible to try to collapse 512MB).
>
> Well, assume you have a VM at that is 2 GiB and could use 4 THPs. It's
> stupid, but there might be some selected use cases where it's not completely
> stupid.
I guess we limit the stupidity by MADV_COLLAPSE working on a PMD-aligned range
so it'll be a no-op for an attempt to collapse 2 MiB (unless I'm misreading the
code).
But it is a bit weird to think that users might assume they will get some
benefit in collapsing a range and in this case would not.
Anyway 64 KiB page sizes throws up a lot worse issues than this (e.g., page
blocks + water marks) so this is tip of the iceberg for that.
>
> --
> Cheers,
>
> David / dhildenb
>
>
next prev parent reply other threads:[~2025-06-25 10:15 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-06-25 1:40 Baolin Wang
2025-06-25 1:40 ` [PATCH v4 1/2] mm: huge_memory: disallow hugepages if the system-wide THP sysfs " Baolin Wang
2025-06-25 4:34 ` Dev Jain
2025-06-25 1:40 ` [PATCH v4 2/2] mm: shmem: disallow hugepages if the system-wide shmem " Baolin Wang
2025-06-25 5:53 ` [PATCH v4 0/2] fix MADV_COLLAPSE issue if THP " Hugh Dickins
2025-06-25 6:05 ` Dev Jain
2025-06-25 6:26 ` Baolin Wang
2025-06-25 6:49 ` Dev Jain
2025-06-25 6:55 ` Baolin Wang
2025-06-25 7:20 ` Lorenzo Stoakes
2025-06-25 7:34 ` David Hildenbrand
2025-06-25 7:55 ` Lorenzo Stoakes
2025-06-25 8:12 ` Lorenzo Stoakes
2025-06-25 8:24 ` David Hildenbrand
2025-06-25 8:37 ` Lorenzo Stoakes
2025-06-25 8:52 ` Baolin Wang
2025-06-25 9:31 ` Lorenzo Stoakes
2025-06-25 10:02 ` Baolin Wang
2025-06-25 10:07 ` David Hildenbrand
2025-06-25 10:15 ` Lorenzo Stoakes [this message]
2025-06-25 10:29 ` David Hildenbrand
2025-06-25 8:53 ` David Hildenbrand
2025-06-25 11:03 ` Usama Arif
2025-06-25 11:09 ` David Hildenbrand
2025-06-26 3:49 ` Hugh Dickins
2025-06-25 7:23 ` David Hildenbrand
2025-06-25 7:30 ` Lorenzo Stoakes
2025-06-25 7:36 ` David Hildenbrand
2025-06-25 7:42 ` Lorenzo Stoakes
2025-06-25 7:49 ` David Hildenbrand
2025-06-25 8:16 ` David Hildenbrand
2025-06-25 8:22 ` Lorenzo Stoakes
2025-06-25 8:40 ` David Hildenbrand
2025-06-25 8:45 ` Lorenzo Stoakes
2025-06-25 21:51 ` Hugh Dickins
2025-07-09 12:36 ` Lorenzo Stoakes
2025-07-10 1:58 ` Baolin Wang
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