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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1uRASO-0000000G1Xl-1KQa; Mon, 16 Jun 2025 14:05:04 +0000 Date: Mon, 16 Jun 2025 15:05:04 +0100 From: Matthew Wilcox To: Bharata B Rao Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Jonathan.Cameron@huawei.com, dave.hansen@intel.com, gourry@gourry.net, hannes@cmpxchg.org, mgorman@techsingularity.net, mingo@redhat.com, peterz@infradead.org, raghavendra.kt@amd.com, riel@surriel.com, rientjes@google.com, sj@kernel.org, weixugc@google.com, ying.huang@linux.alibaba.com, ziy@nvidia.com, dave@stgolabs.net, nifan.cxl@gmail.com, xuezhengchu@huawei.com, yiannis@zptcorp.com, akpm@linux-foundation.org, david@redhat.com Subject: page_ext and memdescs Message-ID: References: <20250616133931.206626-1-bharata@amd.com> <20250616133931.206626-4-bharata@amd.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250616133931.206626-4-bharata@amd.com> X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: A6A0BC0018 X-Stat-Signature: etis1snqxaw74b69fhf54e3wua1szzo5 X-HE-Tag: 1750082711-30702 X-HE-Meta: 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 df3eximJ R57exoCuw7H6vpjjCNeFqRRkj8wkSk0nJvzc/c+BQw8BHmJ3+PSRGx6rQvtQ2u3FtAmCena7taIP67y1XHUKU8Mo7jnkKxOoqnh8rSPBBonITeg4S5yvKt9hx7lD9jUyXt5z/tn4m7pSuxz3P+tR88uEHGS1HpsP+L4DDorzFEh4+4fkjYP8RTps39pJnvKNkMCFnbat1iUkTFyfs6bdVJddHrJPRSJWEHB1CdMgR4c1LzjwzaybCgvS0yMp7eiVkqZ/IKy8Vpgw9VZHWjGvfR6lmjh478980XBy4nPfPUdRQNbe+ytEGcUvTrZRMHu6vPuoe8nQafIu7J5fevDNUNDto3q/YN8k9sAN7 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, Jun 16, 2025 at 07:09:30PM +0530, Bharata B Rao wrote: > diff --git a/include/linux/page_ext.h b/include/linux/page_ext.h > index 76c817162d2f..4300c9dbafec 100644 > --- a/include/linux/page_ext.h > +++ b/include/linux/page_ext.h > @@ -40,8 +40,25 @@ enum page_ext_flags { > PAGE_EXT_YOUNG, > PAGE_EXT_IDLE, > #endif > + /* > + * 32 bits following this are used by the migrator. > + * The next available bit position is 33. > + */ > + PAGE_EXT_MIGRATE_READY, > }; > > +#define PAGE_EXT_MIG_NID_WIDTH 10 > +#define PAGE_EXT_MIG_FREQ_WIDTH 3 > +#define PAGE_EXT_MIG_TIME_WIDTH 18 > + > +#define PAGE_EXT_MIG_NID_SHIFT (PAGE_EXT_MIGRATE_READY + 1) > +#define PAGE_EXT_MIG_FREQ_SHIFT (PAGE_EXT_MIG_NID_SHIFT + PAGE_EXT_MIG_NID_WIDTH) > +#define PAGE_EXT_MIG_TIME_SHIFT (PAGE_EXT_MIG_FREQ_SHIFT + PAGE_EXT_MIG_FREQ_WIDTH) > + > +#define PAGE_EXT_MIG_NID_MASK ((1UL << PAGE_EXT_MIG_NID_SHIFT) - 1) > +#define PAGE_EXT_MIG_FREQ_MASK ((1UL << PAGE_EXT_MIG_FREQ_SHIFT) - 1) > +#define PAGE_EXT_MIG_TIME_MASK ((1UL << PAGE_EXT_MIG_TIME_SHIFT) - 1) OK, so we need to have a conversation about page_ext. Sorry this is happening to you. I've kind of skipped over page_ext when talking about folios and memdescs up to now, so it's not that you've missed anything. As the comment says, * Page Extension can be considered as an extended mem_map. and we need to do this because we don't want to grow struct page beyond 64 bytes. But memdescs are dynamically allocated, so we don't need page_ext any more, and all that code can go away. lib/alloc_tag.c:struct page_ext_operations page_alloc_tagging_ops = { mm/page_ext.c:static struct page_ext_operations page_idle_ops __initdata = { mm/page_ext.c:static struct page_ext_operations *page_ext_ops[] __initdata = { mm/page_owner.c:struct page_ext_operations page_owner_ops = { mm/page_table_check.c:struct page_ext_operations page_table_check_ops = { I think all of these are actually per-memdesc thangs and not per-page things, so we can get rid of them all. That means I don't want to see new per-page data being added to page_ext. So, what's this really used for? It seems like it's really per-allocation, not per-page. Does it need to be preserved across alloc/free or can it be reset at free time?