From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id A6AE8C44500 for ; Tue, 7 Jul 2026 08:27:30 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 9721C6B00B1; Tue, 7 Jul 2026 04:27:29 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 9220C6B00B3; Tue, 7 Jul 2026 04:27:29 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 812F26B00B4; Tue, 7 Jul 2026 04:27:29 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 51BB06B00B1 for ; Tue, 7 Jul 2026 04:27:29 -0400 (EDT) Received: from smtpin22.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay02.hostedemail.com (Postfix) with ESMTP id CB04712038E for ; Tue, 7 Jul 2026 08:27:28 +0000 (UTC) X-FDA: 84961301376.22.BE9C5A0 Received: from out-173.mta0.migadu.com (out-173.mta0.migadu.com [91.218.175.173]) by imf17.hostedemail.com (Postfix) with ESMTP id BADBC40003 for ; Tue, 7 Jul 2026 08:27:26 +0000 (UTC) Authentication-Results: imf17.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=YVTrCYc1; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf17.hostedemail.com: domain of baoquan.he@linux.dev designates 91.218.175.173 as permitted sender) smtp.mailfrom=baoquan.he@linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1783412846; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=xV6i/G5pvlleZ0L2NE10sfLpZZEgkyaYGlgJlwxedI0=; b=mSuavQtH5vX6r8OgfJkDT3SF3QopXol096SpEiNi3+gfVKLnEo94A2bVpN4GS3uLOkMeZr 3l8yXgLKDceAAp+0kSTW76zOrKGF/ZI8HPrq6dLHmYOOpv6/ApfmjSVyIuIDC9GJ/+bAP5 gcjOWCoEXG6ocJFUfj3EVNJ6bdxpHb0= ARC-Authentication-Results: i=1; imf17.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=YVTrCYc1; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf17.hostedemail.com: domain of baoquan.he@linux.dev designates 91.218.175.173 as permitted sender) smtp.mailfrom=baoquan.he@linux.dev ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1783412846; b=uxHUlmb5l2fe/5SlOZK0VpkonCqzVxzmUGb4nqPOrTp1lbJH1OWVjpSWgT1axhKFPvzJWI hEa2zCoguqclGgxj6ZNhdXLahCeJ6uZVuEcs6J8pBQt8P0+KPONLCxXBVnvqgeXEPi7T1O kQCc2Q+bIQNRDEkFRluZ9OZRjbMWQSQ= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1783412845; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=xV6i/G5pvlleZ0L2NE10sfLpZZEgkyaYGlgJlwxedI0=; b=YVTrCYc1lk6biMb7/w3lGOo9ySjGlkCD96RgvbGRfxiWzBgO1Ut3rtMJofaE7o5gakhUkL HSCh/0bijy5lD28vCiOnxnR6cYkN9ZN8rKnitcM2mp6/cdmjYXLO8KMIM6a3XxSVr12wTW aAXhK3h22QY7XfE0HQLbHZHirouHW9U= From: Baoquan He To: linux-mm@kvack.org Cc: akpm@linux-foundation.org, chrisl@kernel.org, kasong@tencent.com, shikemeng@huaweicloud.com, nphamcs@gmail.com, baohua@kernel.org, youngjun.park@lge.com, hannes@cmpxchg.org, yosry@kernel.org, chengming.zhou@linux.dev, linux-kernel@vger.kernel.org, Baoquan He Subject: [RFC PATCH 07/10] mm/page_io: forward ghost swap reads to physical device via Redirect Date: Tue, 7 Jul 2026 16:26:09 +0800 Message-ID: <20260707082614.95030-8-baoquan.he@linux.dev> In-Reply-To: <20260707082614.95030-1-baoquan.he@linux.dev> References: <20260707082614.95030-1-baoquan.he@linux.dev> MIME-Version: 1.0 Content-type: text/plain Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: BADBC40003 X-Stat-Signature: czrbbwczf4i4icmnfu6esh738w7f74th X-HE-Tag: 1783412846-276257 X-HE-Meta: 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 AtMec+M5 3+3nkaLXsD3awaPaUl4mgPdb7FTFeN8CDdD0DBUOZu9xHTL6Ryh9hqFoBMQFv5iFnjv8qlK2CwaICHZdH6Z8wgH9KURT7xlpnIak/EggOO8KElJq07FFqv5MYNmaQDlvEpq/XrpOTIHIlr3BUuTh68GCirtGQnirK88YawaKBMYdbUC2fXJwWOrgEfwdeGcs2busqtGd5FItt9HKmLCulOk8oBLjU30yxOO8VEdLbtwa9REYwphKPjI3edg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: When swap_read_folio() encounters a ghost swap entry (SWP_GHOST), check if there is a Redirect mapping to a physical swap slot via ghost_redirect_to_phys(). If a physical backing exists, forward the I/O to that device: 1. Query the redirect_xa / swap table for the physical swp_entry_t. 2. Temporarily redirect folio->swap to the physical entry so the existing swap_read_folio_bdev_{sync,async} / swap_read_folio_fs path computes the correct sector from the physical offset. 3. Restore folio->swap to the original ghost entry after I/O. This completes the backend-switching round trip: - Swapout: PTE -> ghost entry -> zswap_store -> Pointer(zswap_entry) - Writeback: Pointer -> decompress -> write to phys -> Redirect(phys) - Swapin: PTE -> ghost entry -> Redirect -> read from phys device Signed-off-by: Baoquan He --- mm/page_io.c | 33 +++++++++++++++++++++++++++++++++ 1 file changed, 33 insertions(+) diff --git a/mm/page_io.c b/mm/page_io.c index 96e776f9a503..b87b46f05b2f 100644 --- a/mm/page_io.c +++ b/mm/page_io.c @@ -697,6 +697,39 @@ void swap_read_folio(struct folio *folio, struct swap_iocb **plug, void *zentry) goto finish; if (unlikely(sis->flags & SWP_GHOST)) { + swp_entry_t phys_entry; + struct swap_info_struct *phys_si; + + /* + * Ghost swap entry: check if there's a Redirect to a + * physical swap slot. If so, read from the physical + * device instead. + */ + phys_entry = ghost_redirect_to_phys(sis, swp_offset(folio->swap)); + if (phys_entry.val) { + phys_si = __swap_entry_to_info(phys_entry); + if (phys_si && phys_si->bdev) { + swp_entry_t saved = folio->swap; + + /* + * Temporarily point the folio to the + * physical entry so the bdev read path + * computes the correct sector. + */ + folio->swap = phys_entry; + zswap_folio_swapin(folio); + if (data_race(phys_si->flags & SWP_FS_OPS)) + swap_read_folio_fs(folio, plug); + else if (phys_si->flags & SWP_SYNCHRONOUS_IO) + swap_read_folio_bdev_sync(folio, + phys_si); + else + swap_read_folio_bdev_async(folio, + phys_si); + folio->swap = saved; + goto finish; + } + } folio_unlock(folio); goto finish; } -- 2.54.0