linux-kernel - Re: [PATCH v2 1/3] erofs: get rid of magical Z_EROFS_MAPPING

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Message-ID: <20201208084904.GA3060163@xiangao.remote.csb>
Date:   Tue, 8 Dec 2020 16:49:04 +0800
From:   Gao Xiang <hsiangkao@...hat.com>
To:     Chao Yu <yuchao0@...wei.com>
Cc:     linux-erofs@...ts.ozlabs.org, LKML <linux-kernel@...r.kernel.org>,
        Chao Yu <chao@...nel.org>
Subject: Re: [PATCH v2 1/3] erofs: get rid of magical Z_EROFS_MAPPING_STAGING

On Tue, Dec 08, 2020 at 04:44:12PM +0800, Chao Yu wrote:
> Hi Xiang,

...

> > 
> > I discussed this case in the original thread,
> > https://lore.kernel.org/r/20200519100612.GA3687@hsiangkao-HP-ZHAN-66-Pro-G1
> > 
> > The previous conclusion is that for EROFS case (see Matthew's reply) this
> > pair won't have too much usage. since EROFS pattern saves extra page
> > reference count (- and +) by cases.
> 
> Alright, I see.

Yeah, yet in order for further confusion (or questions from others), let me
update to use this pair as much as possible in the next version :( (If someone
breaks in the future, I may need to remind him in time though...)

> 

...

> 
> Reviewed-by: Chao Yu <yuchao0@...wei.com>

Thanks for the review!

Thanks,
Gao Xiang

> 
> Thanks,
> 
> > 
> > Thanks,
> > Gao Xiang
> > 
> > > 
> > > Thanks,
> > > 
> > > >    		}
> > > > @@ -648,12 +649,12 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
> > > >    retry:
> > > >    	err = z_erofs_attach_page(clt, page, page_type);
> > > > -	/* should allocate an additional staging page for pagevec */
> > > > +	/* should allocate an additional short-lived page for pagevec */
> > > >    	if (err == -EAGAIN) {
> > > >    		struct page *const newpage =
> > > >    				alloc_page(GFP_NOFS | __GFP_NOFAIL);
> > > > -		newpage->mapping = Z_EROFS_MAPPING_STAGING;
> > > > +		set_page_private(newpage, Z_EROFS_SHORTLIVED_PAGE);
> > > >    		err = z_erofs_attach_page(clt, newpage,
> > > >    					  Z_EROFS_PAGE_TYPE_EXCLUSIVE);
> > > >    		if (!err)
> > > > @@ -710,6 +711,11 @@ static void z_erofs_decompress_kickoff(struct z_erofs_decompressqueue *io,
> > > >    		queue_work(z_erofs_workqueue, &io->u.work);
> > > >    }
> > > > +static bool z_erofs_page_is_invalidated(struct page *page)
> > > > +{
> > > > +	return !page->mapping && !z_erofs_is_shortlived_page(page);
> > > > +}
> > > > +
> > > >    static void z_erofs_decompressqueue_endio(struct bio *bio)
> > > >    {
> > > >    	tagptr1_t t = tagptr_init(tagptr1_t, bio->bi_private);
> > > > @@ -722,7 +728,7 @@ static void z_erofs_decompressqueue_endio(struct bio *bio)
> > > >    		struct page *page = bvec->bv_page;
> > > >    		DBG_BUGON(PageUptodate(page));
> > > > -		DBG_BUGON(!page->mapping);
> > > > +		DBG_BUGON(z_erofs_page_is_invalidated(page));
> > > >    		if (err)
> > > >    			SetPageError(page);
> > > > @@ -795,9 +801,9 @@ static int z_erofs_decompress_pcluster(struct super_block *sb,
> > > >    		/* all pages in pagevec ought to be valid */
> > > >    		DBG_BUGON(!page);
> > > > -		DBG_BUGON(!page->mapping);
> > > > +		DBG_BUGON(z_erofs_page_is_invalidated(page));
> > > > -		if (z_erofs_put_stagingpage(pagepool, page))
> > > > +		if (z_erofs_put_shortlivedpage(pagepool, page))
> > > >    			continue;
> > > >    		if (page_type == Z_EROFS_VLE_PAGE_TYPE_HEAD)
> > > > @@ -831,9 +837,9 @@ static int z_erofs_decompress_pcluster(struct super_block *sb,
> > > >    		/* all compressed pages ought to be valid */
> > > >    		DBG_BUGON(!page);
> > > > -		DBG_BUGON(!page->mapping);
> > > > +		DBG_BUGON(z_erofs_page_is_invalidated(page));
> > > > -		if (!z_erofs_page_is_staging(page)) {
> > > > +		if (!z_erofs_is_shortlived_page(page)) {
> > > >    			if (erofs_page_is_managed(sbi, page)) {
> > > >    				if (!PageUptodate(page))
> > > >    					err = -EIO;
> > > > @@ -858,7 +864,7 @@ static int z_erofs_decompress_pcluster(struct super_block *sb,
> > > >    			overlapped = true;
> > > >    		}
> > > > -		/* PG_error needs checking for inplaced and staging pages */
> > > > +		/* PG_error needs checking for all non-managed pages */
> > > >    		if (PageError(page)) {
> > > >    			DBG_BUGON(PageUptodate(page));
> > > >    			err = -EIO;
> > > > @@ -897,8 +903,8 @@ static int z_erofs_decompress_pcluster(struct super_block *sb,
> > > >    		if (erofs_page_is_managed(sbi, page))
> > > >    			continue;
> > > > -		/* recycle all individual staging pages */
> > > > -		(void)z_erofs_put_stagingpage(pagepool, page);
> > > > +		/* recycle all individual short-lived pages */
> > > > +		(void)z_erofs_put_shortlivedpage(pagepool, page);
> > > >    		WRITE_ONCE(compressed_pages[i], NULL);
> > > >    	}
> > > > @@ -908,10 +914,10 @@ static int z_erofs_decompress_pcluster(struct super_block *sb,
> > > >    		if (!page)
> > > >    			continue;
> > > > -		DBG_BUGON(!page->mapping);
> > > > +		DBG_BUGON(z_erofs_page_is_invalidated(page));
> > > > -		/* recycle all individual staging pages */
> > > > -		if (z_erofs_put_stagingpage(pagepool, page))
> > > > +		/* recycle all individual short-lived pages */
> > > > +		if (z_erofs_put_shortlivedpage(pagepool, page))
> > > >    			continue;
> > > >    		if (err < 0)
> > > > @@ -1011,13 +1017,17 @@ static struct page *pickup_page_for_submission(struct z_erofs_pcluster *pcl,
> > > >    	mapping = READ_ONCE(page->mapping);
> > > >    	/*
> > > > -	 * unmanaged (file) pages are all locked solidly,
> > > > +	 * file-backed online pages in plcuster are all locked steady,
> > > >    	 * therefore it is impossible for `mapping' to be NULL.
> > > >    	 */
> > > >    	if (mapping && mapping != mc)
> > > >    		/* ought to be unmanaged pages */
> > > >    		goto out;
> > > > +	/* directly return for shortlived page as well */
> > > > +	if (z_erofs_is_shortlived_page(page))
> > > > +		goto out;
> > > > +
> > > >    	lock_page(page);
> > > >    	/* only true if page reclaim goes wrong, should never happen */
> > > > @@ -1062,8 +1072,8 @@ static struct page *pickup_page_for_submission(struct z_erofs_pcluster *pcl,
> > > >    out_allocpage:
> > > >    	page = erofs_allocpage(pagepool, gfp | __GFP_NOFAIL);
> > > >    	if (!tocache || add_to_page_cache_lru(page, mc, index + nr, gfp)) {
> > > > -		/* non-LRU / non-movable temporary page is needed */
> > > > -		page->mapping = Z_EROFS_MAPPING_STAGING;
> > > > +		/* turn into temporary page if fails */
> > > > +		set_page_private(page, Z_EROFS_SHORTLIVED_PAGE);
> > > >    		tocache = false;
> > > >    	}
> > > > diff --git a/fs/erofs/zdata.h b/fs/erofs/zdata.h
> > > > index 68c9b29fc0ca..b503b353d4ab 100644
> > > > --- a/fs/erofs/zdata.h
> > > > +++ b/fs/erofs/zdata.h
> > > > @@ -173,6 +173,7 @@ static inline void z_erofs_onlinepage_endio(struct page *page)
> > > >    	v = atomic_dec_return(u.o);
> > > >    	if (!(v & Z_EROFS_ONLINEPAGE_COUNT_MASK)) {
> > > > +		set_page_private(page, 0);
> > > >    		ClearPagePrivate(page);
> > > >    		if (!PageError(page))
> > > >    			SetPageUptodate(page);
> > > > 
> > > 
> > 
> > .
> > 
>