Commit 6aaa7b06 authored by Gao Xiang's avatar Gao Xiang
Browse files

erofs: get rid of magical Z_EROFS_MAPPING_STAGING 

Previously, we played around with magical page->mapping for short-lived
temporary pages since we need to identify different types of pages in
the same pcluster but both invalidated and short-lived temporary pages
can have page->mapping == NULL. It was considered as safe because that
temporary pages are all non-LRU / non-movable pages.

This patch tends to use specific page->private to identify short-lived
pages instead so it won't rely on page->mapping anymore. Details are
described in "compress.h" as well.

Link: https://lore.kernel.org/r/20201208095834.3133565-1-hsiangkao@redhat.com


Reviewed-by: default avatarChao Yu <yuchao0@huawei.com>
Signed-off-by: default avatarGao Xiang <hsiangkao@redhat.com>
parent a426ce9d

fs/erofs/compress.h

+38 −13
Original line number Diff line number Diff line
@@ -26,30 +26,55 @@ struct z_erofs_decompress_req { 
	bool inplace_io, partial_decoding;

};



/* some special page->private (unsigned long, see below) */

#define Z_EROFS_SHORTLIVED_PAGE		(-1UL << 2)



/*

 * - 0x5A110C8D ('sallocated', Z_EROFS_MAPPING_STAGING) -

 * used to mark temporary allocated pages from other

 * file/cached pages and NULL mapping pages.

 * For all pages in a pcluster, page->private should be one of

 * Type                         Last 2bits      page->private

 * short-lived page             00              Z_EROFS_SHORTLIVED_PAGE

 * cached/managed page          00              pointer to z_erofs_pcluster

 * online page (file-backed,    01/10/11        sub-index << 2 | count

 *              some pages can be used for inplace I/O)

 *

 * page->mapping should be one of

 * Type                 page->mapping

 * short-lived page     NULL

 * cached/managed page  non-NULL or NULL (invalidated/truncated page)

 * online page          non-NULL

 *

 * For all managed pages, PG_private should be set with 1 extra refcount,

 * which is used for page reclaim / migration.

 */

#define Z_EROFS_MAPPING_STAGING         ((void *)0x5A110C8D)



/* check if a page is marked as staging */

static inline bool z_erofs_page_is_staging(struct page *page)

/*

 * short-lived pages are pages directly from buddy system with specific

 * page->private (no need to set PagePrivate since these are non-LRU /

 * non-movable pages and bypass reclaim / migration code).

 */

static inline bool z_erofs_is_shortlived_page(struct page *page)

{

	return page->mapping == Z_EROFS_MAPPING_STAGING;

	if (page->private != Z_EROFS_SHORTLIVED_PAGE)

		return false;



	DBG_BUGON(page->mapping);

	return true;

}



static inline bool z_erofs_put_stagingpage(struct list_head *pagepool,

static inline bool z_erofs_put_shortlivedpage(struct list_head *pagepool,

					      struct page *page)

{

	if (!z_erofs_page_is_staging(page))

	if (!z_erofs_is_shortlived_page(page))

		return false;



	/* staging pages should not be used by others at the same time */

	if (page_ref_count(page) > 1)

	/* short-lived pages should not be used by others at the same time */

	if (page_ref_count(page) > 1) {

		put_page(page);

	else

	} else {

		/* follow the pcluster rule above. */

		set_page_private(page, 0);

		list_add(&page->lru, pagepool);

	}

	return true;

}

fs/erofs/decompressor.c

+1 −1
Original line number Diff line number Diff line
@@ -76,7 +76,7 @@ static int z_erofs_lz4_prepare_destpages(struct z_erofs_decompress_req *rq, 
			victim = erofs_allocpage(pagepool, GFP_KERNEL);

			if (!victim)

				return -ENOMEM;

			victim->mapping = Z_EROFS_MAPPING_STAGING;

			set_page_private(victim, Z_EROFS_SHORTLIVED_PAGE);

		}

		rq->out[i] = victim;

	}

fs/erofs/zdata.c

+31 −26
Original line number Diff line number Diff line
@@ -226,11 +226,8 @@ int erofs_try_to_free_all_cached_pages(struct erofs_sb_info *sbi, 


		/* barrier is implied in the following 'unlock_page' */

		WRITE_ONCE(pcl->compressed_pages[i], NULL);

		set_page_private(page, 0);

		ClearPagePrivate(page);



		detach_page_private(page);

		unlock_page(page);

		put_page(page);

	}

	return 0;

}
@@ -254,10 +251,8 @@ int erofs_try_to_free_cached_page(struct address_space *mapping, 
		}

		erofs_workgroup_unfreeze(&pcl->obj, 1);



		if (ret) {

			ClearPagePrivate(page);

			put_page(page);

		}

		if (ret)

			detach_page_private(page);

	}

	return ret;

}
@@ -648,12 +643,12 @@ hitted: 


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 +705,11 @@ 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 +722,7 @@ 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 +795,9 @@ 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 +831,9 @@ 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 +858,7 @@ 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 +897,8 @@ out: 
		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 +908,10 @@ out: 
		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 +1011,17 @@ repeat: 
	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 +1066,8 @@ repeat: 
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;

	}
@@ -1080,8 +1084,9 @@ out_allocpage: 
	}



	if (tocache) {

		set_page_private(page, (unsigned long)pcl);

		SetPagePrivate(page);

		attach_page_private(page, pcl);

		/* drop a ref added by allocpage (then we have 2 refs here) */

		put_page(page);

	}

out:	/* the only exit (for tracing and debugging) */

	return page;

fs/erofs/zdata.h

+1 −0
Original line number Diff line number Diff line
@@ -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);

CRA Git | Maintained and supported by SUSTech CRA and CCSE