From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kara Subject: Re: [PATCH] ext4: fix checking on nr_to_write Date: Tue, 15 Oct 2013 14:34:39 +0200 Message-ID: <20131015123439.GC12428@quack.suse.cz> References: <1381682393-5769-1-git-send-email-ming.lei@canonical.com> <20131014125858.GH19604@quack.suse.cz> <20131014173459.GL19604@quack.suse.cz> <20131015102553.22d4a018@tom-ThinkPad-T410> <20131015103900.GB12428@quack.suse.cz> <20131015191556.50c3eb03@tom-ThinkPad-T410> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Jan Kara , Linux Kernel Mailing List , Ted Tso , linux-ext4@vger.kernel.org, "linux-fsdevel@vger.kernel.org" , Ming Lei To: Ming Lei Return-path: Content-Disposition: inline In-Reply-To: <20131015191556.50c3eb03@tom-ThinkPad-T410> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Tue 15-10-13 19:15:56, Ming Lei wrote: > > This won't quite work because if the page is fully mapped > > mpage_process_page_bufs() will immediately submit the page and decrease > > nr_to_write. So now you would end up writing less than you were asked for > > in some cases. > > Yes, your are right, so how about below? > > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c > index 32c04ab..3cf7abb 100644 > --- a/fs/ext4/inode.c > +++ b/fs/ext4/inode.c > @@ -2295,6 +2295,7 @@ static int mpage_prepare_extent_to_map(struct mpage_da_data *mpd) > struct address_space *mapping = mpd->inode->i_mapping; > struct pagevec pvec; > unsigned int nr_pages; > + int left = mpd->wbc->nr_to_write; 'long' please. Otherwise the patch looks fine. Thanks! Honza > pgoff_t index = mpd->first_page; > pgoff_t end = mpd->last_page; > int tag; > @@ -2330,6 +2331,17 @@ static int mpage_prepare_extent_to_map(struct mpage_da_data *mpd) > if (page->index > end) > goto out; > > + /* > + * Accumulated enough dirty pages? This doesn't apply > + * to WB_SYNC_ALL mode. For integrity sync we have to > + * keep going because someone may be concurrently > + * dirtying pages, and we might have synced a lot of > + * newly appeared dirty pages, but have not synced all > + * of the old dirty pages. > + */ > + if (mpd->wbc->sync_mode == WB_SYNC_NONE && left <= 0) > + goto out; > + > /* If we can't merge this page, we are done. */ > if (mpd->map.m_len > 0 && mpd->next_page != page->index) > goto out; > @@ -2364,19 +2376,7 @@ static int mpage_prepare_extent_to_map(struct mpage_da_data *mpd) > if (err <= 0) > goto out; > err = 0; > - > - /* > - * Accumulated enough dirty pages? This doesn't apply > - * to WB_SYNC_ALL mode. For integrity sync we have to > - * keep going because someone may be concurrently > - * dirtying pages, and we might have synced a lot of > - * newly appeared dirty pages, but have not synced all > - * of the old dirty pages. > - */ > - if (mpd->wbc->sync_mode == WB_SYNC_NONE && > - mpd->next_page - mpd->first_page >= > - mpd->wbc->nr_to_write) > - goto out; > + left--; > } > pagevec_release(&pvec); > cond_resched(); > > > > Attached patch should do what's needed. Can you try whether > > it fixes the problem for you (it seems to work OK in my testing). > > In fact, I had wrote and tested your attached patch before my last post, > and it may trigger BUG() in mpage_release_unused_pages(), that is because > we touch mpd->next_page without locking current page, so it is better to > not increase mpd->next_page if the current page won't be processed. > > > Thanks, > -- > Ming Lei -- Jan Kara SUSE Labs, CR