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b=EWOgEUft+aw3zsyNgDtc5duH/DEazLb4DieB37uLtHP1Gs4fAWRfpL3LP6Zv0buDB me6oi+y3tCxnJusH1neeV5+j2XO7Mz8lqki6Oz1b688sX1t8vWhM+XSQdzzqZq9b4l L2KrIWjoPcVhrgkwsdba+k94EUnhhps1huoi7gdqrCXsC4IAhQaLwAMzPqMdv0QOEA GLQyHh+dc+35P6lCJQ76TWiSa2SN5hllsMNZ4evmlScoQPt5drh69YGGVfTX+Dc0er 7J6UePi3RlcKpbLmoBSQs+pkYp+1ZkXuVEa1pdYNfT7m+z3xzRbJFh8+N/MeKmrDnp Alq28rmhZ79gw== Message-ID: Date: Thu, 9 Apr 2026 14:26:31 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: =?UTF-8?B?UmU6IOetlOWkjTogW1BBVENIIHYzIDIvMl0ga3NtOiBPcHRpbWl6ZSBy?= =?UTF-8?Q?map=5Fwalk=5Fksm_by_passing_a_suitable_address_range?= From: "David Hildenbrand (Arm)" To: xu.xin16@zte.com.cn, shr@devkernel.io, ljs@kernel.org Cc: hughd@google.com, akpm@linux-foundation.org, chengming.zhou@linux.dev, wang.yaxin@zte.com.cn, yang.yang29@zte.com.cn, michel@lespinasse.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260409185610930gKQqJsFs5KoTU4S8MrflI@zte.com.cn> Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 5C3BE40005 X-Stat-Signature: 1peowchdqgn6z7esha3tecup614sn8hz X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1775737597-430051 X-HE-Meta: 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 nbhWnes7 LhZ3kw4xji9NtzAvofUCw92C/qZQeuDIKXYR/Jq26Wr1+Aozl/y7RNcrU2YbqElUz05AJ9fK8yhERhOAJFKDK0xtucEDkHcejxgOkfMW4IH7ZvE/Uuo3lt0F4kLVRlBd2BarwIsF71Ke0vHGa7JcKPomlYZ29CmoMPPDmURmQXm8QOxfAwYMdrl0U1Vln1fIE0/yh7kcnZ9VV2Nir2RB3sMdsHIlsvSoqchE14TzAxKWOSyBvh+izZHofmQZGKP3UOepIXSd4qp9cSqvZOhVDYSpO+rfeF8+HkOdw6r6kCUWBVJTRIgTDYB0wJtuJnjVGwGtQ68dd0fMtmq8Nd8pBVfeppjzYDOr0eHga Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 4/9/26 13:59, David Hildenbrand (Arm) wrote: > On 4/9/26 12:56, xu.xin16@zte.com.cn wrote: >>> >>> Hmm, maybe we could do the following. I think the other members are only >>> relevant for the unstable tree. >> >> Well, I suspect that "SmartScan-Related" members might be also needed and used even when >> >> it's a stable rmap_item. In should_skip_rmap_item(), if its page is KSM, it can't be skip. > > Yes, needs some more thought on details. We might have to ignore/skip > the fields for stable tree entries that have not a KSM page. > >> >> What if the rmap_item is stable, but its page is not KSM? > > I guess that would happen if we had a rmap_item at that address, and > then changed the page (e.g., COW). > > ksm_do_scan() would call cmp_and_merge_page() after obtaining such an > rmap item from scan_get_next_rmap_item(). > > In cmp_and_merge_page() we'd call remove_rmap_item_from_tree() and > recalculate the checksum. > > In remove_rmap_item_from_tree() we remove the item from the stable tree. > > So we'd want to ignore the entries in STABLE_FLAG in > scan_get_next_rmap_item() to then reinitialize the fields in > cmp_and_merge_page() after remove_rmap_item_from_tree() I guess. > Something like this on top: diff --git a/mm/ksm.c b/mm/ksm.c index 0c6bfed280f7..51fd37ee24d6 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -905,6 +905,8 @@ static void remove_node_from_stable_tree(struct ksm_stable_node *stable_node) VM_BUG_ON(stable_node->rmap_hlist_len <= 0); stable_node->rmap_hlist_len--; put_anon_vma(rmap_item->anon_vma); + /* Reset pgoff that overlays age-related information. */ + rmap_item->pgoff = 0; rmap_item->address &= PAGE_MASK; cond_resched(); } @@ -1058,9 +1060,10 @@ static void remove_rmap_item_from_tree(struct ksm_rmap_item *rmap_item) stable_node->rmap_hlist_len--; put_anon_vma(rmap_item->anon_vma); + /* Reset pgoff that overlays age-related information. */ + rmap_item->pgoff = 0; rmap_item->head = NULL; rmap_item->address &= PAGE_MASK; - } else if (rmap_item->address & UNSTABLE_FLAG) { unsigned char age; /* @@ -2465,6 +2468,10 @@ static bool should_skip_rmap_item(struct folio *folio, if (folio_test_ksm(folio)) return false; + /* There is no age information in stable-tree nodes. */ + if (rmap_item->address & STABLE_FLAG) + return false; + age = rmap_item->age; if (age != U8_MAX) rmap_item->age++; But it's all confusing. Because we might temporarily have rmap_item->anon_vma set on an rmap_entry that does not yet have the STABLE_FLAG flag set through stable_tree_append(). And then we magically call break_cow() which does a magical put_anon_vma(rmap_item->anon_vma); (this doesn't look correct in once case) ... anyhow. So we might want to reset the pgoff there as well, OR only store the pgoff in stable_tree_append() where we actually set STABLE_FLAG. -- Cheers, David