From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1EB6A1FB7 for ; Fri, 25 Mar 2022 01:13:38 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D1DA0C340EC; Fri, 25 Mar 2022 01:13:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1648170817; bh=1+c7G0iIHC1u7fAlZ10RX8tSDjNAa1xxcZ6EfqUb/sE=; h=Date:To:From:In-Reply-To:Subject:From; b=HjvAzmHaa2T3OGLBrGqaa0CLAyXtFIBVN67InZS4Rz5M7tExAqW+IgiAsjbNm183D +X37qIGvh3IvqlQy4LwSJxcwSx4nEUIZUfjm5EbAOKRAoD1Yrmlgf6QHHds02Pavl2 2034+huGRiwnSVN+0Ddme+5tJWPjWpVuTgRXIXgI= Date: Thu, 24 Mar 2022 18:13:37 -0700 To: zhangliang5@huawei.com,willy@infradead.org,vbabka@suse.cz,shy828301@gmail.com,shakeelb@google.com,rppt@linux.ibm.com,roman.gushchin@linux.dev,rientjes@google.com,riel@surriel.com,peterx@redhat.com,oleg@redhat.com,nadav.amit@gmail.com,mike.kravetz@oracle.com,mhocko@kernel.org,kirill.shutemov@linux.intel.com,jhubbard@nvidia.com,jgg@nvidia.com,jannh@google.com,jack@suse.cz,hughd@google.com,hch@lst.de,ddutile@redhat.com,aarcange@redhat.com,david@redhat.com,akpm@linux-foundation.org,patches@lists.linux.dev,linux-mm@kvack.org,mm-commits@vger.kernel.org,torvalds@linux-foundation.org,akpm@linux-foundation.org From: Andrew Morton In-Reply-To: <20220324180758.96b1ac7e17675d6bc474485e@linux-foundation.org> Subject: [patch 101/114] mm: slightly clarify KSM logic in do_swap_page() Message-Id: <20220325011337.D1DA0C340EC@smtp.kernel.org> Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: From: David Hildenbrand Subject: mm: slightly clarify KSM logic in do_swap_page() Let's make it clearer that KSM might only have to copy a page in case we have a page in the swapcache, not if we allocated a fresh page and bypassed the swapcache. While at it, add a comment why this is usually necessary and merge the two swapcache conditions. [akpm@linux-foundation.org: fix comment, per David] Link: https://lkml.kernel.org/r/20220131162940.210846-4-david@redhat.com Signed-off-by: David Hildenbrand Acked-by: Vlastimil Babka Cc: Andrea Arcangeli Cc: Christoph Hellwig Cc: David Rientjes Cc: Don Dutile Cc: Hugh Dickins Cc: Jan Kara Cc: Jann Horn Cc: Jason Gunthorpe Cc: John Hubbard Cc: Kirill A. Shutemov Cc: Liang Zhang Cc: Matthew Wilcox (Oracle) Cc: Michal Hocko Cc: Mike Kravetz Cc: Mike Rapoport Cc: Nadav Amit Cc: Oleg Nesterov Cc: Peter Xu Cc: Rik van Riel Cc: Roman Gushchin Cc: Shakeel Butt Cc: Yang Shi Signed-off-by: Andrew Morton --- mm/memory.c | 36 ++++++++++++++++++++++-------------- 1 file changed, 22 insertions(+), 14 deletions(-) --- a/mm/memory.c~mm-slightly-clarify-ksm-logic-in-do_swap_page +++ a/mm/memory.c @@ -3607,21 +3607,29 @@ vm_fault_t do_swap_page(struct vm_fault goto out_release; } - /* - * Make sure try_to_free_swap or reuse_swap_page or swapoff did not - * release the swapcache from under us. The page pin, and pte_same - * test below, are not enough to exclude that. Even if it is still - * swapcache, we need to check that the page's swap has not changed. - */ - if (unlikely((!PageSwapCache(page) || - page_private(page) != entry.val)) && swapcache) - goto out_page; + if (swapcache) { + /* + * Make sure try_to_free_swap or swapoff did not release the + * swapcache from under us. The page pin, and pte_same test + * below, are not enough to exclude that. Even if it is still + * swapcache, we need to check that the page's swap has not + * changed. + */ + if (unlikely(!PageSwapCache(page) || + page_private(page) != entry.val)) + goto out_page; - page = ksm_might_need_to_copy(page, vma, vmf->address); - if (unlikely(!page)) { - ret = VM_FAULT_OOM; - page = swapcache; - goto out_page; + /* + * KSM sometimes has to copy on read faults, for example, if + * page->index of !PageKSM() pages would be nonlinear inside the + * anon VMA -- PageKSM() is lost on actual swapout. + */ + page = ksm_might_need_to_copy(page, vma, vmf->address); + if (unlikely(!page)) { + ret = VM_FAULT_OOM; + page = swapcache; + goto out_page; + } } cgroup_throttle_swaprate(page, GFP_KERNEL); _