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Unverified Commit 8ccbd0ca authored by Gao Xiang's avatar Gao Xiang Committed by Michael Bestas
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UPSTREAM: erofs: complete a missing case for inplace I/O 

Add a missing case which could cause unnecessary page allocation but
not directly use inplace I/O instead, which increases runtime extra
memory footprint.

The detail is, considering an online file-backed page, the right half
of the page is chosen to be cached (e.g. the end page of a readahead
request) and some of its data doesn't exist in managed cache, so the
pcluster will be definitely kept in the submission chain. (IOWs, it
cannot be decompressed without I/O, e.g., due to the bypass queue).

Currently, DELAYEDALLOC/TRYALLOC cases can be downgraded as NOINPLACE,
and stop online pages from inplace I/O. After this patch, unneeded page
allocations won't be observed in pickup_page_for_submission() then.

Link: https://lore.kernel.org/r/20210321183227.5182-1-hsiangkao@aol.com


Signed-off-by: default avatarGao Xiang <hsiangkao@redhat.com>

Bug: 201372112
Change-Id: I639279e87b749b8625d2a8e77055a9fc52073542
(cherry picked from commit 0b964600d3aae56ff9d5bdd710a79f39a44c572c)
Signed-off-by: default avatarHuang Jianan <huangjianan@oppo.com>
parent 5c4e6ce1

fs/erofs/zdata.c

+29 −15
Original line number Diff line number Diff line
@@ -104,6 +104,12 @@ enum z_erofs_collectmode { 
	 * |_______PRIMARY_FOLLOWED_______|________PRIMARY_HOOKED___________|

	 */

	COLLECT_PRIMARY_HOOKED,

	/*

	 * a weak form of COLLECT_PRIMARY_FOLLOWED, the difference is that it

	 * could be dispatched into bypass queue later due to uptodated managed

	 * pages. All related online pages cannot be reused for inplace I/O (or

	 * pagevec) since it can be directly decoded without I/O submission.

	 */

	COLLECT_PRIMARY_FOLLOWED_NOINPLACE,

	/*

	 * The current collection has been linked with the owned chain, and
@@ -185,22 +191,26 @@ static void preload_compressed_pages(struct z_erofs_collector *clt, 


		if (page) {

			t = tag_compressed_page_justfound(page);

		} else if (type == DELAYEDALLOC) {

			t = tagptr_init(compressed_page_t, PAGE_UNALLOCATED);

		} else if (type == TRYALLOC) {

		} else {

			/* I/O is needed, no possible to decompress directly */

			standalone = false;

			switch (type) {

			case DELAYEDALLOC:

				t = tagptr_init(compressed_page_t,

						PAGE_UNALLOCATED);

				break;

			case TRYALLOC:

				newpage = erofs_allocpage(pagepool, gfp);

				if (!newpage)

				goto dontalloc;



			set_page_private(newpage, Z_EROFS_PREALLOCATED_PAGE);

					continue;

				set_page_private(newpage,

						 Z_EROFS_PREALLOCATED_PAGE);

				t = tag_compressed_page_justfound(newpage);

		} else {	/* DONTALLOC */

dontalloc:

			if (standalone)

				clt->compressedpages = pages;

			standalone = false;

				break;

			default:        /* DONTALLOC */

				continue;

			}

		}



		if (!cmpxchg_relaxed(pages, NULL, tagptr_cast_ptr(t)))

			continue;
@@ -213,7 +223,11 @@ static void preload_compressed_pages(struct z_erofs_collector *clt, 
		}

	}



	if (standalone)		/* downgrade to PRIMARY_FOLLOWED_NOINPLACE */

	/*

	 * don't do inplace I/O if all compressed pages are available in

	 * managed cache since it can be moved to the bypass queue instead.

	 */

	if (standalone)

		clt->mode = COLLECT_PRIMARY_FOLLOWED_NOINPLACE;

}