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b=LjnPMOIP5C99X8WAMf59MwKO6YCUExvkThrlOsLYDyQBSyKMQd6tFJV0zwILESpQw BErK7G4mTNIlhxRXMh8vbTiNZW348f2u1L8NrZr5ChgAGhSJKPoUg1bX8PYNVoXiO8 BU9pcso8wGIEnUgfxusuTsAtA6jbdzDOoTjU4xORAnAo5W4xHjl6GoqLX1xntagMOR DQZ6FpWCWysWc5yxTjhP/IQHGa5iXdHhnSihzM+UsF+o2hdhQz82vgeiHvfbwiLsTK iAEI/MPclxreW/sCxtpbg11wTkJgs4Ky0+cK57+2jQsAI5ylO0PhbqTIbataBQlldi SoZjoWi/U/KaQ== Date: Tue, 4 Nov 2025 19:18:14 +0200 From: Mike Rapoport To: Akinobu Mita , Dan Williams Cc: linux-cxl@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org Subject: Re: [PATCH] memblock: fix memblock_estimated_nr_free_pages() for soft-reserved memory Message-ID: References: <20251104003921.9707-1-akinobu.mita@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251104003921.9707-1-akinobu.mita@gmail.com> X-Rspamd-Server: rspam12 X-Rspam-User: X-Rspamd-Queue-Id: 73A4C14000B X-Stat-Signature: 3ya64pyaw4bbz6qyjybz64absgq54677 X-HE-Tag: 1762276701-447702 X-HE-Meta: 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 P4Em8l4h RwsJbujAK/t6Ea22LSNwM2zC0dq7glpJ30SdUXVD7sr7ysxGObjFJ+MgaFaaHaiIARrDNMTfhn80Ijdos4+wTYz50Q3fQlT0jSaLv4VosySj+gXiAdsJ0QAmOqX1LmjFvexicWbZVkl/Lap2lRjQTCP4eCk8/PMT5qHCEaMYfZv8JPhJA/7lbs3WX2/01sLAiD8aSX7rZZzEz2xMzstNeqk8gtwykOSz+7x+WtQM1EY92DPMoAtk8B1M41ICs0saKPTjfWP8nUr9cfnA/KZrIUp6e7AE8b4dANrsDRRg5Z+vbyxfwwKoysKLroX4HdQkQHoyW3KC9ZM5bUrWnbiR5q22vYEbz1W8zoWGDzsVN/ySOpHuZuI9DgfwSJ9f5h62rhqcOVga65/+EY1I= 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: (added Dan Williams) Hi, On Tue, Nov 04, 2025 at 09:39:21AM +0900, Akinobu Mita wrote: > memblock_estimated_nr_free_pages() returns the difference between the total > size of the "memory" memblock type and the "reserved" memblock type. > > The "soft-reserved" memory regions are added to the "reserved" memblock > type, but not to the "memory" memblock type. Therefore, @Dan, do we really need to memblock_reserve() the E820_TYPE_SOFT_RESERVED ranges? Quick scan didn't show anything that requires this, but I could easily miss something. > memblock_estimated_nr_free_pages() may return a smaller value than > expected, or if it underflows, an extremely large value. > > /proc/sys/kernel/threads-max is determined by the value of > memblock_estimated_nr_free_pages(). This issue was discovered on machines > with CXL memory because kernel.threads-max was either smaller than expected > or extremely large for the installed DRAM size. > > This fixes the issue by improving the accuracy of > memblock_estimated_nr_free_pages() by subtracting only the overlapping size > of regions with "memory" and "reserved" memblock types. > > Signed-off-by: Akinobu Mita > --- > mm/memblock.c | 33 ++++++++++++++++++++++++++++++++- > 1 file changed, 32 insertions(+), 1 deletion(-) > > diff --git a/mm/memblock.c b/mm/memblock.c > index e23e16618e9b..af014fa10a44 100644 > --- a/mm/memblock.c > +++ b/mm/memblock.c ... > @@ -1826,7 +1842,22 @@ phys_addr_t __init_memblock memblock_reserved_kern_size(phys_addr_t limit, int n > */ > unsigned long __init memblock_estimated_nr_free_pages(void) > { > - return PHYS_PFN(memblock_phys_mem_size() - memblock_reserved_size()); We have memblock_reserved_kern_size() that tells how much memory was reserved from the actual RAM. Replacing memblock_reserved_size() with memblock_reserved_kern_size() will omit "soft-reserved" ranges. > + int memory_idx, reserved_idx; > + struct memblock_type *memory_type = &memblock.memory; > + struct memblock_type *reserved_type = &memblock.reserved; > + struct memblock_region *memory_region, *reserved_region; > + phys_addr_t phys_mem_size = 0; > + > + for_each_memblock_type(memory_idx, memory_type, memory_region) { > + phys_mem_size += memory_region->size; > + for_each_memblock_type(reserved_idx, reserved_type, reserved_region) { > + phys_mem_size -= memblock_addrs_overlap_size(memory_region->base, > + memory_region->size, reserved_region->base, > + reserved_region->size); > + } > + } > + > + return PHYS_PFN(phys_mem_size); > } > > /* lowest address */ > -- > 2.43.0 > -- Sincerely yours, Mike.