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 X-Spam-Level: X-Spam-Status: No, score=-3.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A5354C61DD8 for ; Mon, 16 Nov 2020 15:14:56 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 000FC221F9 for ; Mon, 16 Nov 2020 15:14:55 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="pD234fux" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 000FC221F9 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 7A6F96B005C; Mon, 16 Nov 2020 10:14:55 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 72F4B6B006C; Mon, 16 Nov 2020 10:14:55 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5F6E06B006E; Mon, 16 Nov 2020 10:14:55 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0221.hostedemail.com [216.40.44.221]) by kanga.kvack.org (Postfix) with ESMTP id 28BB16B005C for ; Mon, 16 Nov 2020 10:14:55 -0500 (EST) Received: from smtpin12.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 875C51EF1 for ; Mon, 16 Nov 2020 15:14:54 +0000 (UTC) X-FDA: 77490628908.12.club41_500221d27329 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin12.hostedemail.com (Postfix) with ESMTP id 5E4A918054902 for ; Mon, 16 Nov 2020 15:14:54 +0000 (UTC) X-HE-Tag: club41_500221d27329 X-Filterd-Recvd-Size: 8299 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf09.hostedemail.com (Postfix) with ESMTP for ; Mon, 16 Nov 2020 15:14:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=DPK8kltl3zjX8pqHlBtk1g1ne4D5St7jwKhxm4gTJu8=; b=pD234fuxwp9moQ14SJrs0DTB8C dfmEyPxIbX33wEVNG0/I85yb+JcIY206Y77Aipblvnf6Bvu3Gyz6ivCMj6IcXW48auThCxpnrNjkz IooTapSSZ5NPzrvyGQO93iM0ymePG+SitxcNefJYyvMRPq15mvMk0X+Au80/8pWK2F5qulB2l3DV1 L0Sbtq0C7e+xEptFt46fWYINu89PaOPAmWMgVDNEbM2mICyfVT4bCGJefPCfB8SetLbmuGQ9f1yAK Ut8qZUb/vZid5oYxOnk0/iq1D5QxgnvkH4vvNjpTtXwLXtO/pMYR0Mxr5YF0R5/2+An7JxVWZWfbS Y8sf4bAg==; Received: from willy by casper.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1kegDM-0006Uh-HT; Mon, 16 Nov 2020 15:14:44 +0000 Date: Mon, 16 Nov 2020 15:14:44 +0000 From: Matthew Wilcox To: Hugh Dickins Cc: Andrew Morton , Jan Kara , William Kucharski , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, hch@lst.de, hannes@cmpxchg.org, yang.shi@linux.alibaba.com, dchinner@redhat.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 00/16] Overhaul multi-page lookups for THP Message-ID: <20201116151444.GB29991@casper.infradead.org> References: <20201112212641.27837-1-willy@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Nov 16, 2020 at 02:34:34AM -0800, Hugh Dickins wrote: > On Thu, 12 Nov 2020, Matthew Wilcox (Oracle) wrote: > > > This THP prep patchset changes several page cache iteration APIs to only > > return head pages. > > > > - It's only possible to tag head pages in the page cache, so only > > return head pages, not all their subpages. > > - Factor a lot of common code out of the various batch lookup routines > > - Add mapping_seek_hole_data() > > - Unify find_get_entries() and pagevec_lookup_entries() > > - Make find_get_entries only return head pages, like find_get_entry(). > > > > These are only loosely connected, but they seem to make sense together > > as a series. > > > > v4: > > - Add FGP_ENTRY, remove find_get_entry and find_lock_entry > > - Rename xas_find_get_entry to find_get_entry > > - Add "Optimise get_shadow_from_swap_cache" > > - Move "iomap: Use mapping_seek_hole_data" to this patch series > > - Rebase against next-20201112 > > I hope next-20201112 had nothing vital for this series, I applied > it to v5.10-rc3, and have been busy testing huge tmpfs on that. Thank you. It's plain I'm not able to hit these cases ... I do run xfstests against shmem, but that's obviously not good enough. Can you suggest something I should be running to improve my coverage? > Fix to [PATCH v4 06/16] mm/filemap: Add helper for finding pages. > I hit that VM_BUG_ON_PAGE(!thp_contains) when swapping, it is not > safe without page lock, during the interval when shmem is moving a > page between page cache and swap cache. It could be tightened by > passing in a new FGP to distinguish whether searching page or swap > cache, but I think never tight enough in the swap case - because there > is no rule for persisting page->private as there is for page->index. > The best I could do is: I'll just move this out to the caller who actually locks the page: +++ b/mm/filemap.c @@ -1839,7 +1839,6 @@ static inline struct page *find_get_entry(struct xa_state *xas, pgoff_t max, put_page(page); goto reset; } - VM_BUG_ON_PAGE(!thp_contains(page, xas->xa_index), page); return page; reset: @@ -1923,6 +1922,8 @@ unsigned find_lock_entries(struct address_space *mapping, pgoff_t start, goto put; if (page->mapping != mapping || PageWriteback(page)) goto unlock; + VM_BUG_ON_PAGE(!thp_contains(page, xas->xa_index), + page); } indices[pvec->nr] = xas.xa_index; if (!pagevec_add(pvec, page)) > Fix to [PATCH v4 07/16] mm/filemap: Add mapping_seek_hole_data. > Crashed on a swap entry 0x2ff09, fairly obvious... Whoops. Thanks. > Fix to [PATCH v4 15/16] mm/truncate,shmem: Handle truncates that split THPs. > One machine ran fine, swapping and building in ext4 on loop0 on huge tmpfs; > one machine got occasional pages of zeros in its .os; one machine couldn't > get started because of ext4_find_dest_de errors on the newly mkfs'ed fs. > The partial_end case was decided by PAGE_SIZE, when there might be a THP > there. The below patch has run well (for not very long), but I could > easily have got it slightly wrong, off-by-one or whatever; and I have > not looked into the similar code in mm/truncate.c, maybe that will need > a similar fix or maybe not. > > --- 5103w/mm/shmem.c 2020-11-12 15:46:21.075254036 -0800 > +++ 5103wh/mm/shmem.c 2020-11-16 01:09:35.431677308 -0800 > @@ -874,7 +874,7 @@ static void shmem_undo_range(struct inod > long nr_swaps_freed = 0; > pgoff_t index; > int i; > - bool partial_end; > + bool same_page; > > if (lend == -1) > end = -1; /* unsigned, so actually very big */ > @@ -907,16 +907,12 @@ static void shmem_undo_range(struct inod > index++; > } > > - partial_end = ((lend + 1) % PAGE_SIZE) > 0; > + same_page = (lstart >> PAGE_SHIFT) == end; > page = NULL; > shmem_getpage(inode, lstart >> PAGE_SHIFT, &page, SGP_READ); > if (page) { > - bool same_page; > - > page = thp_head(page); > same_page = lend < page_offset(page) + thp_size(page); > - if (same_page) > - partial_end = false; I don't object to this patch at all, at least partly because it's shorter and simpler! I don't understand what it's solving, though. The case where there's a THP which covers partial_end is supposed to be handled by the three lines above. > Fix to [PATCH v4 15/16] mm/truncate,shmem: Handle truncates that split THPs. > xfstests generic/012 on huge tmpfs hit this every time (when checking > xfs_io commands available: later decides "not run" because no "fiemap"). > I grabbed this line unthinkingly from one of your later series, it fixes > the crash; but once I actually thought about it when trying to track down > weirder behaviours, realize that the kmap_atomic() and flush_dcache_page() > in zero_user_segments() are not prepared for a THP - so highmem and > flush_dcache_page architectures will be disappointed. If I searched > through your other series, I might find the complete fix; or perhaps > it's already there in linux-next, I haven't looked. zero_user_segments() is fixed by "mm: Support THPs in zero_user_segments". I think most recently posted here: https://lore.kernel.org/linux-mm/20201026183136.10404-2-willy@infradead.org/ My fault for not realising this patch depended on that patch. I did test these patches stand-alone, but it didn't trigger this problem. flush_dcache_page() needs to be called once for each sub-page. We really need a flush_dcache_thp() so that architectures can optimise this. Although maybe now that's going to be called flush_dcache_folio(). > I also had noise from the WARN_ON(page_to_index(page) != index) > in invalidate_inode_pages2_range(): but that's my problem, since > for testing I add a dummy shmem_direct_IO() (return 0): for that > I've now added a shmem_mapping() check at the head of pages2_range(). Ah, I have a later fix for invalidate_inode_pages2_range(): https://lore.kernel.org/linux-mm/20201026183136.10404-6-willy@infradead.org/ I didn't post it earlier because there aren't any filesystems currently which use THPs and directIO ;-) > That's all for now: I'll fire off more overnight testing. Thanks!