From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-99.freemail.mail.aliyun.com (out30-99.freemail.mail.aliyun.com [115.124.30.99]) (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 839582566 for ; Sat, 13 Sep 2025 03:26:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.99 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757733988; cv=none; b=r25B2FD6aSvSMX2cbxUTHUj+BEQhphMEHLp1P/PCCQDLgkLqjrpa4eIe48MjhW0H0xPZpsBl6G2URtVUEfgXxaG5szS+GEAQUOVdIyywqY5gGmLSTvwavCeDF+EpkK/lr3unE3/wI9HIzaGSaFxs4SjG7oSUIMezvSLtatvzXEI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757733988; c=relaxed/simple; bh=ufXIhhGNY61fv/ll3s+7ydHirPh1AzwivwLHtinBWOo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=dlllAiyEkdOjmI3DaMHKcRZ7Xdpf3iw7BMLXCmQNSuTeKUMQgeJgaWhzamTBta7NIWTuTJwJ394aziljd+GmBrVQVyO/RUaU6yAO6sMn68OXOFEF8IRwONmDWEF2zM3+ErlJqXF0OXLr3cvC23z5K7CTYdWFdq64twZPdYtaY3s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=s8lMUvZN; arc=none smtp.client-ip=115.124.30.99 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="s8lMUvZN" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1757733984; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=LBPemiQvLMxvPRaP1xaM0T1pppLLfrD8DNU0toXcXBo=; b=s8lMUvZNXSVQg4/b/wF+xJThTetnZEhAtxWpj7Y+zhMuUr6JFGkoBv3r4pcuL+hOebIMB65UGZI9826i4ydw0vQpYDNcuvsDmwrjtFgMWdyk2dCl1Y9553dbR4bcW/CmbmAuHJ52CkhntrbTiarBDpMYHoEy/rpD9NBS2rdV+M0= Received: from 30.134.50.220(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0Wnse-95_1757733982 cluster:ay36) by smtp.aliyun-inc.com; Sat, 13 Sep 2025 11:26:23 +0800 Message-ID: <59ddf3bc-cfc0-40ab-ae2d-859724ef6168@linux.alibaba.com> Date: Sat, 13 Sep 2025 11:26:22 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 09/15] mm/shmem, swap: remove redundant error handling for replacing folio To: Kairui Song Cc: linux-mm@kvack.org, Andrew Morton , Matthew Wilcox , Hugh Dickins , Chris Li , Barry Song , Baoquan He , Nhat Pham , Kemeng Shi , Ying Huang , Johannes Weiner , David Hildenbrand , Yosry Ahmed , Lorenzo Stoakes , Zi Yan , linux-kernel@vger.kernel.org References: <20250910160833.3464-1-ryncsn@gmail.com> <20250910160833.3464-10-ryncsn@gmail.com> <0cb2bc82-1957-4efe-8c85-8558743dcf80@linux.alibaba.com> From: Baolin Wang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 2025/9/12 20:36, Kairui Song wrote: > On Fri, Sep 12, 2025 at 4:22 PM Baolin Wang > wrote: >> On 2025/9/11 00:08, Kairui Song wrote: >>> From: Kairui Song >>> >>> Shmem may replace a folio in the swap cache if the cached one doesn't >>> fit the swapin's GFP zone. When doing so, shmem has already double >>> checked that the swap cache folio is locked, still has the swap cache >>> flag set, and contains the wanted swap entry. So it is impossible to >>> fail due to an XArray mismatch. There is even a comment for that. >>> >>> Delete the defensive error handling path, and add a WARN_ON instead: >>> if that happened, something has broken the basic principle of how the >>> swap cache works, we should catch and fix that. >>> >>> Signed-off-by: Kairui Song >>> Reviewed-by: David Hildenbrand >>> --- >>> mm/shmem.c | 42 ++++++++++++------------------------------ >>> 1 file changed, 12 insertions(+), 30 deletions(-) >>> >>> diff --git a/mm/shmem.c b/mm/shmem.c >>> index 410f27bc4752..5f395fab489c 100644 >>> --- a/mm/shmem.c >>> +++ b/mm/shmem.c >>> @@ -1661,13 +1661,13 @@ int shmem_writeout(struct folio *folio, struct swap_iocb **plug, >>> } >>> >>> /* >>> - * The delete_from_swap_cache() below could be left for >>> + * The swap_cache_del_folio() below could be left for >>> * shrink_folio_list()'s folio_free_swap() to dispose of; >>> * but I'm a little nervous about letting this folio out of >>> * shmem_writeout() in a hybrid half-tmpfs-half-swap state >>> * e.g. folio_mapping(folio) might give an unexpected answer. >>> */ >>> - delete_from_swap_cache(folio); >>> + swap_cache_del_folio(folio); >>> goto redirty; >>> } >>> if (nr_pages > 1) >>> @@ -2045,7 +2045,7 @@ static struct folio *shmem_swap_alloc_folio(struct inode *inode, >>> new->swap = entry; >>> >>> memcg1_swapin(entry, nr_pages); >>> - shadow = get_shadow_from_swap_cache(entry); >>> + shadow = swap_cache_get_shadow(entry); >> >> Again, there are still some issues with the patch split. The swapcache >> related APIs replacement should be placed in Patch 8, otherwise there >> will be buidling errors after applying Patch 8. >> >> With this issue fixed: >> Reviewed-by: Baolin Wang >> > > Hi Baolin > > Yeah you are right, I need to move these few changes to patch 8. > > BTW I also found that the WARN_ON and irq unlock needs following fix, > the stats update need to be done with irq disabled: Yes, indeed, I overlooked this. > diff --git a/mm/shmem.c b/mm/shmem.c > index 957e40caba6e..c4d491c93506 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -2121,14 +2121,14 @@ static int shmem_replace_folio(struct folio > **foliop, gfp_t gfp, > /* Swap cache still stores N entries instead of a high-order entry */ > xa_lock_irq(&swap_mapping->i_pages); > for (i = 0; i < nr_pages; i++) { > - WARN_ON_ONCE(xas_store(&xas, new)); > + WARN_ON_ONCE(xas_store(&xas, new) != old); > xas_next(&xas); > } > - xa_unlock_irq(&swap_mapping->i_pages); > > mem_cgroup_replace_folio(old, new); > shmem_update_stats(new, nr_pages); > shmem_update_stats(old, -nr_pages); > + xa_unlock_irq(&swap_mapping->i_pages); > > folio_add_lru(new); > *foliop = new;