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Wed, 06 Aug 2025 07:31:04 -0700 (PDT) Date: Wed, 6 Aug 2025 14:31:03 +0000 From: Wei Yang To: Sumanth Korikkar Cc: Wei Yang , Andrew Morton , linux-mm , LKML , David Hildenbrand , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , linux-s390 Subject: Re: [PATCH v2] mm: fix accounting of memmap pages for early sections Message-ID: <20250806143103.xkdz4sinbhcq4vyd@master> Reply-To: Wei Yang References: <20250804151328.2326642-1-sumanthk@linux.ibm.com> <20250806090320.wdt4zsfiambtgkvy@master> Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170113 (1.7.2) On Wed, Aug 06, 2025 at 02:46:43PM +0200, Sumanth Korikkar wrote: >> The change here is reasonable. While maybe we still miss the counting at some >> other points. >> >> For example: >> >> a. >> >> sparse_init_nid() >> __populate_section_memmap() >> >> If !CONFIG_SPARSEMEM_VMEMMAP, and sparse_buffer_alloc() return NULL, it >> allocate extra memory from bootmem, which looks not counted. > >Currently, the accounting is done upfront in sparse_buffer_init(), where >memmap_boot_pages_add() is called for !CONFIG_SPARSEMEM_VMEMMAP. > >The function sparse_buffer_alloc() can return NULL in two scenarios: > >* During sparse_buffer_init(), if memmap_alloc() fails, sparsemap_buf will be NULL. >* Inside sparse_buffer_alloc(), if ptr + size exceeds sparsemap_buf_end, > then ptr is set to NULL. > >Considering this, perhaps memmap_boot_pages_add() could be moved into >__populate_section_memmap(), with the accounting done only if the >operation is successful. What do you think? > Looks reasonable to me. >> section_activate() >> populate_section_memmap() >> >> If !CONFIG_SPARSEMEM_VMEMMAP, it just call kvmalloc_node(), which looks not >> counted. > >Sounds right. This means nr_memmap_pages adjustment is needed for >!CONFIG_SPARSEMEM_VMEMMAP here. I will recheck this. > >Thank you -- Wei Yang Help you, Help me