+ fs-isofs-replace-kmap-with-kmap_local_page.patch added to mm-nonmm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain, Size: 5599 bytes --]


The patch titled
     Subject: fs/isofs: replace kmap() with kmap_local_page()
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     fs-isofs-replace-kmap-with-kmap_local_page.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/fs-isofs-replace-kmap-with-kmap_local_page.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: "Fabio M. De Francesco" <fmdefrancesco@gmail.com>
Subject: fs/isofs: replace kmap() with kmap_local_page()
Date: Mon, 1 Aug 2022 14:27:09 +0200

The use of kmap() is being deprecated in favor of kmap_local_page().

There are two main problems with kmap(): (1) It comes with an overhead as
mapping space is restricted and protected by a global lock for
synchronization and (2) it also requires global TLB invalidation when the
kmap's pool wraps and it might block when the mapping space is fully
utilized until a slot becomes available.

With kmap_local_page() the mappings are per thread, CPU local, can take
page faults, and can be called from any context (including interrupts). 
Tasks can be preempted and, when scheduled to run again, the kernel
virtual addresses are restored and still valid.  It is faster than kmap()
in kernels with HIGHMEM enabled.

Since kmap_local_page() can be safely used in compress.c, it should be
called everywhere instead of kmap().

Therefore, replace kmap() with kmap_local_page() in compress.c.  Where it
is needed, use memzero_page() instead of open coding kmap_local_page()
plus memset() to fill the pages with zeros.  Delete the redundant
flush_dcache_page() in the two call sites of memzero_page().

Tested with mkisofs on a QEMU/KVM x86_32 VM, 6GB RAM, booting a kernel
with HIGHMEM64GB enabled.

Link: https://lkml.kernel.org/r/20220801122709.8164-1-fmdefrancesco@gmail.com
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Suggested-by: Ira Weiny <ira.weiny@intel.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Pali Rohár <pali@kernel.org>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/isofs/compress.c |   20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

--- a/fs/isofs/compress.c~fs-isofs-replace-kmap-with-kmap_local_page
+++ a/fs/isofs/compress.c
@@ -67,8 +67,7 @@ static loff_t zisofs_uncompress_block(st
 		for ( i = 0 ; i < pcount ; i++ ) {
 			if (!pages[i])
 				continue;
-			memset(page_address(pages[i]), 0, PAGE_SIZE);
-			flush_dcache_page(pages[i]);
+			memzero_page(pages[i], 0, PAGE_SIZE);
 			SetPageUptodate(pages[i]);
 		}
 		return ((loff_t)pcount) << PAGE_SHIFT;
@@ -120,7 +119,7 @@ static loff_t zisofs_uncompress_block(st
 	       zerr != Z_STREAM_END) {
 		if (!stream.avail_out) {
 			if (pages[curpage]) {
-				stream.next_out = page_address(pages[curpage])
+				stream.next_out = kmap_local_page(pages[curpage])
 						+ poffset;
 				stream.avail_out = PAGE_SIZE - poffset;
 				poffset = 0;
@@ -176,6 +175,10 @@ static loff_t zisofs_uncompress_block(st
 				flush_dcache_page(pages[curpage]);
 				SetPageUptodate(pages[curpage]);
 			}
+			if (stream.next_out != (unsigned char *)zisofs_sink_page) {
+				kunmap_local(stream.next_out);
+				stream.next_out = NULL;
+			}
 			curpage++;
 		}
 		if (!stream.avail_in)
@@ -183,6 +186,8 @@ static loff_t zisofs_uncompress_block(st
 	}
 inflate_out:
 	zlib_inflateEnd(&stream);
+	if (stream.next_out && stream.next_out != (unsigned char *)zisofs_sink_page)
+		kunmap_local(stream.next_out);
 
 z_eio:
 	mutex_unlock(&zisofs_zlib_lock);
@@ -283,9 +288,7 @@ static int zisofs_fill_pages(struct inod
 	}
 
 	if (poffset && *pages) {
-		memset(page_address(*pages) + poffset, 0,
-		       PAGE_SIZE - poffset);
-		flush_dcache_page(*pages);
+		memzero_page(*pages, poffset, PAGE_SIZE - poffset);
 		SetPageUptodate(*pages);
 	}
 	return 0;
@@ -343,10 +346,8 @@ static int zisofs_read_folio(struct file
 	for (i = 0; i < pcount; i++, index++) {
 		if (i != full_page)
 			pages[i] = grab_cache_page_nowait(mapping, index);
-		if (pages[i]) {
+		if (pages[i])
 			ClearPageError(pages[i]);
-			kmap(pages[i]);
-		}
 	}
 
 	err = zisofs_fill_pages(inode, full_page, pcount, pages);
@@ -357,7 +358,6 @@ static int zisofs_read_folio(struct file
 			flush_dcache_page(pages[i]);
 			if (i == full_page && err)
 				SetPageError(pages[i]);
-			kunmap(pages[i]);
 			unlock_page(pages[i]);
 			if (i != full_page)
 				put_page(pages[i]);
_

Patches currently in -mm which might be from fmdefrancesco@gmail.com are

hfsplus-unmap-the-page-in-the-fail_page-label.patch
hfsplus-convert-kmap-to-kmap_local_page-in-bnodec.patch
hfsplus-convert-kmap-to-kmap_local_page-in-bitmapc.patch
hfsplus-convert-kmap-to-kmap_local_page-in-btreec.patch
fs-isofs-replace-kmap-with-kmap_local_page.patch