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b=BrB+T16nkVTMYt7xlK0QT3nNBbBQ+u+K50tCW25pJhVN7Tk8vwPMUY6PohUVHQirK Jo8KYGxg5BGZCUOkJA3Bl1g6m4lKrOEK99Z4tKh2Aah2YmetX8SZZ90yEkmLkD65Z4 K8JC/2KDCJwfgxlPArmvmM3oyufCLsftE/evV74sNDUN4gytbYFqRQtbvxO71Xxhgg bda/SQC65qNuJOutl7qu6rWZcHGKXV5WutSxCYxd649o/XUrgEEmUllL/DlriJDShh VsoGofQGL1PgRdBPxkmIdkR2y+Nau7KHQwsMr3VTaSUFbF/1hYlIPlV0q/A4TAGJaQ zGyVf7Hno9FGQ== Date: Sun, 17 May 2026 13:17:50 +0300 From: Mike Rapoport To: Pratyush Yadav Cc: Pasha Tatashin , Alexander Graf , Muchun Song , Oscar Salvador , David Hildenbrand , Andrew Morton , Jason Miu , kexec@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 10/12] kho: extended scratch Message-ID: References: <20260429133928.850721-1-pratyush@kernel.org> <20260429133928.850721-11-pratyush@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260429133928.850721-11-pratyush@kernel.org> X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 9B485140005 X-Rspam-User: X-Stat-Signature: 76f5od8o8pytm8qbp498ryh38duhkzzg X-HE-Tag: 1779013078-864757 X-HE-Meta: U2FsdGVkX1/io0LUEOes2pfYdZdn9Koud4QT2sC0WS2LOvbH00WohaKQe8DDcNODfOZ1yXHBXFGj3U0U6lfbecIwZYSBe+QpwuJpW9lv7Kw0WK59lbL7zMgojC/XhOyROJS01Ya6Y+AUFUfiTHowxN7vEi9anHOweiyt3dZhTfgIrWp2he1DN689G152h1JmiC+v0AszE+3KSJqDCw5BlrsNYAT103sCH8s7mTAQ09dSSo7QMS51AyF03mgvgGqiRkRxFDiRnhwMZhY3F/D9Ao8IFB0xibrWDVyEARoVL57KTUkZDevP8i03EeQl+RKf8Cl0M9TIGblO2xNPnEOHbGtYjzHAJ+dBujSF+CPQAgMSFOUe0od+Vk/sv7DcP6UoHiemTVDu/JF/+deegqwy5V4X9d4PKRvzdjxBgcwL/fn1bH2yW+WJbz1IPOQLkh57FPzujfbQaLtFlwN7GBgGn1rVn6Dun8+FO9ZoKocXYpyWlFnWD9ffFHizc4CzKRJEmYXrc4pt4EpR3E5UB3V9Sm3GwSneiJ13eJU8Pa4EMkmcwnQmGNRAvCVHawe+dJ6sBEg6gU+bSBNEPHUG+BQmznR2Mh+/23YXLrYKB0vvHYM66fu8vuVtKO2+6iCP4NI7v5M/le5wV/bp3Eggc7k0KGU8vJP8YMVP26lgp2FKLo9cjI6nlIlzEwfjjsBkutVf1xbFjyvV51kGNXsIVmmPYSgpAlhjSCyfbue+nqX3hrX1oRrQaBcJFhBeqdcOz3Ugj0cgs+imalU02QgnK8Wg5acXdRzV2HPaE93ipBP5ZmPApqER4kgFCYlCeLiOGLzN7UsPcDQvY6sAO090VzRGJRjmyNsLUsrieBfBsetqoSUAHTntxRD5dxGU1fBUrFvkuIi4ciqr0yjOK/8Y58YbYezOuBGJN3Kat5zR3uSjeLoL7OcX4ncLOHSD7VFoHBjSrjojDwIZEBRRF6pKl2j FDWfBVK/ +SLV/fidDJPWKqF1rYS5uZBG4bIZAWmiXgdJFiK7Y1oABi6tESA4T+UObATEvCr1VpAA1KGocklnt1bTch1VdU2kYgQ9W+qsimVmoEezk5egpqZZWrbMHRej+TUpu2mmfL+w+xsj4QoV+63IyZ5Kyc3r72BYrigoSDYLM4Xer8WUvmlNk1rkl06qAPlP8BwMNw6HqyS09Mi//I/x07mpEa1G9NTP/yVe/rLFcU45jRiaUWuQGVxfG5kFk+BTOw9EhG3e0T3TvY6DfNtvXr6xQPPBkMw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Apr 29, 2026 at 03:39:12PM +0200, Pratyush Yadav wrote: > From: "Pratyush Yadav (Google)" > > Methodology > =========== > > Introduce extended scratch areas. These areas are discovered at boot by > walking the preserved memory radix tree and looking for free blocks of > memory. They then marked as scratch to allow allocations from them. This > makes KHO more resilient to memory pressure and allows supporting huge > page preservation. > > Since the preserved memory radix tree mixes both physical address and > order into a single key, and does not track table pages, it is difficult > to identify free areas from it directly. Walk the tree and digest it > down into another radix tree. The latter tracks blocks of > KHO_EXT_SHIFT (1 GiB as of now) granularity. Then walk the digested tree > and mark the areas between the present keys as scratch. > > Signed-off-by: Pratyush Yadav (Google) > --- > include/linux/kexec_handover.h | 1 + > kernel/liveupdate/kexec_handover.c | 148 +++++++++++++++++++++++++---- > mm/mm_init.c | 1 + > 3 files changed, 133 insertions(+), 17 deletions(-) > > diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c > index 1a04e089f779..c2b843a5fb28 100644 > --- a/kernel/liveupdate/kexec_handover.c > +++ b/kernel/liveupdate/kexec_handover.c > @@ -840,6 +857,120 @@ static void __init kho_reserve_scratch(void) > kho_enable = false; > } > > +#define KHO_EXT_SHIFT 30 /* 1 GiB */ arm64 does not necessarily use 1G gigantic pages and worse, it can have 2 gigantic hstates. I think this should take into account what actual gigantic page sizes are in use for the general case. -- Sincerely yours, Mike.