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AJvYcCXP8vmCa8OqfflmrPNjyZbb1iupgCapE7cvGpX/wk/1oo+cWI0T+acwpw2k+9R9thF+yoZBa0Jeaw==@kvack.org X-Gm-Message-State: AOJu0YyqwEguxSkjgmRqWRRoc6nsEK2JEP0n3OcdAHAwe8ME+75NbQIM toPF99WLu2EIBWyIJsLJexJNTEF1D5EIi4OSyCPEIXx68+NaW5JIdiDj6w/r2nAew7pqhLluxrd zSaRZT02eZ+i4TcTw9VHZ8VWuBH4d1gWKBugn6dOGOg== X-Gm-Gg: ASbGncuwPAcwBmCGROgDvxtNrpESEOWLp/Y7JY/MkQel6UFTahroEzkbcRoneuAmwVT odYhjcfIWzqDdefFLrQSWXCcnJ7xiyC7RV5F2p2uRQk897cxc5cChMPd3xtpEoejoF911n0ZgBP BWp+DnZ/K0hhV3GaPDrFgwXpnllOG67qCelAB/qfCcfq7YnPGvF5s2534T39OJy5HyGLJiEhsUh AFeUp/fzuAtNSkYMz8OyvOaSXeR6q3kI1a9tYC11xBFJjQK/Ogoq790SImnF07h3KR7 X-Google-Smtp-Source: AGHT+IHXgN2A3la0YJxyyXqBd0MasNf9JRFf1RqDDAA3OQ+yqvWzJtnk8lJzn/WVj6Q3Gweop1jcYJMwQr5SF/i4N7Y= X-Received: by 2002:a05:6402:518c:b0:63c:5eef:c8eb with SMTP id 4fb4d7f45d1cf-63c5eefccb8mr7887864a12.31.1760998233475; Mon, 20 Oct 2025 15:10:33 -0700 (PDT) MIME-Version: 1.0 References: <20251018171756.1724191-1-pasha.tatashin@soleen.com> <20251018171756.1724191-10-pasha.tatashin@soleen.com> In-Reply-To: From: Pasha Tatashin Date: Mon, 20 Oct 2025 18:09:57 -0400 X-Gm-Features: AS18NWCJ1e_UpQW7FijpabJLDoZps9ZGHn4yCdktBVEdTDDj_pM8M4yk7V0Wg8M Message-ID: Subject: Re: [PATCH v6 09/10] liveupdate: kho: Increase metadata bitmap size to PAGE_SIZE To: Mike Rapoport Cc: akpm@linux-foundation.org, brauner@kernel.org, corbet@lwn.net, graf@amazon.com, jgg@ziepe.ca, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, masahiroy@kernel.org, ojeda@kernel.org, pratyush@kernel.org, rdunlap@infradead.org, tj@kernel.org, jasonmiu@google.com, dmatlack@google.com, skhawaja@google.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Queue-Id: 11F19C0006 X-Rspamd-Server: rspam03 X-Stat-Signature: z53se6ibrxsmofe7gpbhsbdwcheur8u5 X-HE-Tag: 1760998234-855346 X-HE-Meta: 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 Rv6dplby 1gcMzAARf+Wn67PrLA1QOEoUvPHfYOkDXAkZiVvGJ9WS7fOm76fGG4GN2oyurusODqYSpwVW4LP2SSlFQCKeXkubWPlc7uV622m4t7o62k3PuX/OcE3tQp1l7mCJpIHxrWb6YjOkN5AxuSrMEIvfiyuonbXFiq+cPXKnQjMwMyPNRVCRLwFye3RVOWA76FQ5HQhS0xtjpQnjiss2uT/9BPUxurZj37sJCT2NJZy5HYY+VxUwLd3xJEAdhqT5h8hXzAU7cbdtkNF8/ufQd8yQxUDMWDB93KMGD21ebnbrAe3OTOh8HcEEEkgrhVZ0NpwY6+hzl 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, Oct 20, 2025 at 4:03=E2=80=AFAM Mike Rapoport wro= te: > > On Sat, Oct 18, 2025 at 01:17:55PM -0400, Pasha Tatashin wrote: > > Metadata is preserved via 512-bytes, which requires using slabs. Slabs > > KHO memory preservation metadata is preserved in 512 byte chunks which > requires their allocation from slab allocator. done > > > are not safe to be used with KHO because of kfence, and because partial > > Please add more details why kfence is not safe here. Done. > > > slabs may lead leaks to the next kernel. Change the size to be > > PAGE_SIZE. > > > > While this change could potentially increase metadata overhead on > > systems with sparsely preserved memory, this is being mitigated by > > ongoing work to reduce sparseness during preservation via 1G guest > > pages. Furthermore, this change aligns with future work on a stateless > > KHO, which will also use page-sized bitmaps for its radix tree metadata= . > > With the stateless memory preservation there would be no problem with > kfence, right? > Maybe we should accelerate the stateless preservation work? They are orthogonal, theoretically radix tree could still use the 512-bit bitmaps, but we chose to use page size. Also, Statless KHO still requires some work, and because it requires removing the notifiers, it is better if it is based it on top of the other LUO prep patches. > > > Signed-off-by: Pasha Tatashin > > -- > Sincerely yours, > Mike.