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From: Chengming Zhou Date: Fri, 21 Jun 2024 15:54:29 +0800 Subject: [PATCH v2 1/3] mm/ksm: refactor out try_to_merge_with_zero_page() Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20240621-b4-ksm-scan-optimize-v2-1-1c328aa9e30b@linux.dev> References: <20240621-b4-ksm-scan-optimize-v2-0-1c328aa9e30b@linux.dev> In-Reply-To: <20240621-b4-ksm-scan-optimize-v2-0-1c328aa9e30b@linux.dev> To: Andrew Morton , david@redhat.com, aarcange@redhat.com, hughd@google.com, shr@devkernel.io Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, zhouchengming@bytedance.com, Chengming Zhou X-Developer-Signature: v=1; a=ed25519-sha256; t=1718956503; l=3224; i=chengming.zhou@linux.dev; s=20240617; h=from:subject:message-id; bh=XgUEfBzhfRP/ORf+1yxH34MeMyVcyA4uQSa5dx7WhmQ=; b=MeI/7pIXiWUSInmK68RxchUNLgqfVLCS2dSmEoaOE6psxVMHnvFbf/CCP6m1r9tkrbULcrm3S jcdjyQiAELQCDtQuG372QdBsbsz+DlLVK2VBPccqx3FDGVC5Ymv55y3 X-Developer-Key: i=chengming.zhou@linux.dev; a=ed25519; pk=/XPhIutBo+zyUeQyf4Ni5JYk/PEIWxIeUQqy2DYjmhI= X-Migadu-Flow: FLOW_OUT In preparation for later changes, refactor out a new function called try_to_merge_with_zero_page(), which tries to merge with zero page. Signed-off-by: Chengming Zhou --- mm/ksm.c | 70 ++++++++++++++++++++++++++++++++++++---------------------------- 1 file changed, 40 insertions(+), 30 deletions(-) diff --git a/mm/ksm.c b/mm/ksm.c index 34c4820e0d3d..1427abd18627 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -1531,6 +1531,44 @@ static int try_to_merge_one_page(struct vm_area_struct *vma, return err; } +/* + * This function returns 0 if the pages were merged or if they are + * no longer merging candidates (e.g., VMA stale), -EFAULT otherwise. + */ +static int try_to_merge_with_zero_page(struct ksm_rmap_item *rmap_item, + struct page *page) +{ + struct mm_struct *mm = rmap_item->mm; + int err = -EFAULT; + + /* + * Same checksum as an empty page. We attempt to merge it with the + * appropriate zero page if the user enabled this via sysfs. + */ + if (ksm_use_zero_pages && (rmap_item->oldchecksum == zero_checksum)) { + struct vm_area_struct *vma; + + mmap_read_lock(mm); + vma = find_mergeable_vma(mm, rmap_item->address); + if (vma) { + err = try_to_merge_one_page(vma, page, + ZERO_PAGE(rmap_item->address)); + trace_ksm_merge_one_page( + page_to_pfn(ZERO_PAGE(rmap_item->address)), + rmap_item, mm, err); + } else { + /* + * If the vma is out of date, we do not need to + * continue. + */ + err = 0; + } + mmap_read_unlock(mm); + } + + return err; +} + /* * try_to_merge_with_ksm_page - like try_to_merge_two_pages, * but no new kernel page is allocated: kpage must already be a ksm page. @@ -2306,7 +2344,6 @@ static void stable_tree_append(struct ksm_rmap_item *rmap_item, */ static void cmp_and_merge_page(struct page *page, struct ksm_rmap_item *rmap_item) { - struct mm_struct *mm = rmap_item->mm; struct ksm_rmap_item *tree_rmap_item; struct page *tree_page = NULL; struct ksm_stable_node *stable_node; @@ -2375,36 +2412,9 @@ static void cmp_and_merge_page(struct page *page, struct ksm_rmap_item *rmap_ite return; } - /* - * Same checksum as an empty page. We attempt to merge it with the - * appropriate zero page if the user enabled this via sysfs. - */ - if (ksm_use_zero_pages && (checksum == zero_checksum)) { - struct vm_area_struct *vma; + if (!try_to_merge_with_zero_page(rmap_item, page)) + return; - mmap_read_lock(mm); - vma = find_mergeable_vma(mm, rmap_item->address); - if (vma) { - err = try_to_merge_one_page(vma, page, - ZERO_PAGE(rmap_item->address)); - trace_ksm_merge_one_page( - page_to_pfn(ZERO_PAGE(rmap_item->address)), - rmap_item, mm, err); - } else { - /* - * If the vma is out of date, we do not need to - * continue. - */ - err = 0; - } - mmap_read_unlock(mm); - /* - * In case of failure, the page was not really empty, so we - * need to continue. Otherwise we're done. - */ - if (!err) - return; - } tree_rmap_item = unstable_tree_search_insert(rmap_item, page, &tree_page); if (tree_rmap_item) { -- 2.45.2