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=-17.2 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 DECB8C4361B for ; Fri, 11 Dec 2020 12:02:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 92AB023E21 for ; Fri, 11 Dec 2020 12:02:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2395383AbgLKMCP (ORCPT ); Fri, 11 Dec 2020 07:02:15 -0500 Received: from mx2.suse.de ([195.135.220.15]:33234 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2395292AbgLKMBs (ORCPT ); Fri, 11 Dec 2020 07:01:48 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1607688059; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=ZWl67b7IAXsdpcW2IM/VtNRbguyKCrdW0iuHmncHNk0=; b=jQPv0oAHGEuuf6ztlTvdnbVl7fc0Y32VqG2QdRnAfOE33lgOJYIH0dE+5GpQ1QmyF7GBFs 4QmpETI+BTGUUOdnZbN8G1MahkMuThPlRFdwRn6kc2a6z5Pvx6T527rWbfVoNSHJ3xEWvf 8dSeNL4QkVdGpYCKmdMNFKocIqpYTlQ= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 25F03AEAB; Fri, 11 Dec 2020 12:00:59 +0000 (UTC) Subject: Re: [PATCH v2 12/18] btrfs: extent_io: implement try_release_extent_buffer() for subpage metadata support To: Qu Wenruo , linux-btrfs@vger.kernel.org References: <20201210063905.75727-1-wqu@suse.com> <20201210063905.75727-13-wqu@suse.com> From: Nikolay Borisov Autocrypt: addr=nborisov@suse.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20201210063905.75727-13-wqu@suse.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 10.12.20 г. 8:38 ч., Qu Wenruo wrote: > Unlike the original try_release_extent_buffer, > try_release_subpage_extent_buffer() will iterate through > btrfs_subpage::tree_block_bitmap, and try to release each extent buffer. > > Signed-off-by: Qu Wenruo > --- > fs/btrfs/extent_io.c | 73 ++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 73 insertions(+) > > diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c > index 141e414b1ab9..4d55803302e9 100644 > --- a/fs/btrfs/extent_io.c > +++ b/fs/btrfs/extent_io.c > @@ -6258,10 +6258,83 @@ void memmove_extent_buffer(const struct extent_buffer *dst, > } > } > > +static int try_release_subpage_extent_buffer(struct page *page) > +{ > + struct btrfs_fs_info *fs_info = btrfs_sb(page->mapping->host->i_sb); > + u64 page_start = page_offset(page); > + int bitmap_size = BTRFS_SUBPAGE_BITMAP_SIZE; Remove this variable and directly use BTRFS_SUBPAGE_BITMAP_SIZE as a terminating condition > + int bit_start = 0; > + int ret; > + > + while (bit_start < bitmap_size) { You really want to iterate for a fixed number of items so switch that to a for loop. > + struct btrfs_subpage *subpage; > + struct extent_buffer *eb; > + unsigned long flags; > + u16 tmp = 1 << bit_start; > + u64 start; > + > + /* > + * Make sure the page still has private, as previous run can > + * detach the private > + */ But if previous run has run it would have disposed of this eb and you won't find this page at all, no ? > + spin_lock(&page->mapping->private_lock); > + if (!PagePrivate(page)) { > + spin_unlock(&page->mapping->private_lock); > + break; > + } > + subpage = (struct btrfs_subpage *)page->private; > + spin_unlock(&page->mapping->private_lock); > + > + spin_lock_irqsave(&subpage->lock, flags); > + if (!(tmp & subpage->tree_block_bitmap)) { > + spin_unlock_irqrestore(&subpage->lock, flags); > + bit_start++; > + continue; > + } > + spin_unlock_irqrestore(&subpage->lock, flags); > + > + start = bit_start * fs_info->sectorsize + page_start; > + bit_start += fs_info->nodesize >> fs_info->sectorsize_bits; By doing this you are really saying "skip all blocks pertaining to this eb". In order for this to be correct it would imply that bit_start should _always_ be 0,4,8,12 - am I correct? But what happens if if (!(tmp & subpage->tree_block_bitmap)) has executed and bit_start is now 1, then you'd make start = page_start + 4k , skip next 4(16k) blocks but that would be wrong, no ? Essentially the page would look like: |0|1|2|3|4|5|6|7|8|9|10|11|12|13|14|15 So you want to release the EB's that spawn 0-3, 4-7, 8-11, 12-15, but what if bit_start becomes 1 and you add 4 to that, this offsets all further calculation by 1 i.e you are going into the next eb. > + /* > + * Here we can't call find_extent_buffer() which will increase > + * eb->refs. > + */ > + rcu_read_lock(); > + eb = radix_tree_lookup(&fs_info->buffer_radix, > + start >> fs_info->sectorsize_bits); > + rcu_read_unlock(); > + ASSERT(eb); > + spin_lock(&eb->refs_lock); > + if (atomic_read(&eb->refs) != 1 || extent_buffer_under_io(eb) || > + !test_and_clear_bit(EXTENT_BUFFER_TREE_REF, &eb->bflags)) { > + spin_unlock(&eb->refs_lock); > + continue; > + } > + /* > + * Here we don't care the return value, we will always check > + * the page private at the end. > + * And release_extent_buffer() will release the refs_lock. > + */ > + release_extent_buffer(eb); > + } > + /* Finally to check if we have cleared page private */ > + spin_lock(&page->mapping->private_lock); > + if (!PagePrivate(page)) > + ret = 1; > + else > + ret = 0; > + spin_unlock(&page->mapping->private_lock); > + return ret; > + > +} > + > int try_release_extent_buffer(struct page *page) > { > struct extent_buffer *eb; > > + if (btrfs_sb(page->mapping->host->i_sb)->sectorsize < PAGE_SIZE) > + return try_release_subpage_extent_buffer(page); > + > /* > * We need to make sure nobody is attaching this page to an eb right > * now. >