linux-toradex.git/mm/fadvise.c, branch v5.11

mm, fadvise: improve the expensive remote LRU cache draining after FADV_DONTNEED

2020-10-14T01:38:29+00:00

Our users reported that there're some random latency spikes when their RT
process is running.  Finally we found that latency spike is caused by
FADV_DONTNEED.  Which may call lru_add_drain_all() to drain LRU cache on
remote CPUs, and then waits the per-cpu work to complete.  The wait time
is uncertain, which may be tens millisecond.

That behavior is unreasonable, because this process is bound to a specific
CPU and the file is only accessed by itself, IOW, there should be no
pagecache pages on a per-cpu pagevec of a remote CPU.  That unreasonable
behavior is partially caused by the wrong comparation of the number of
invalidated pages and the number of the target.  For example,

        if (count < (end_index - start_index + 1))

The count above is how many pages were invalidated in the local CPU, and
(end_index - start_index + 1) is how many pages should be invalidated.
The usage of (end_index - start_index + 1) is incorrect, because they are
virtual addresses, which may not mapped to pages.  Besides that, there may
be holes between start and end.  So we'd better check whether there are
still pages on per-cpu pagevec after drain the local cpu, and then decide
whether or not to call lru_add_drain_all().

After I applied it with a hotfix to our production environment, most of
the lru_add_drain_all() can be avoided.

Suggested-by: Mel Gorman 
Signed-off-by: Yafang Shao 
Signed-off-by: Andrew Morton 
Acked-by: Mel Gorman 
Cc: Johannes Weiner 
Link: https://lkml.kernel.org/r/20200923133318.14373-1-laoar.shao@gmail.com
Signed-off-by: Linus Torvalds

mm: return void from various readahead functions

2020-06-02T17:59:06+00:00

ondemand_readahead has two callers, neither of which use the return
value.  That means that both ra_submit and __do_page_cache_readahead()
can return void, and we don't need to worry that a present page in the
readahead window causes us to return a smaller nr_pages than we ought to
have.

Similarly, no caller uses the return value from
force_page_cache_readahead().

Signed-off-by: Matthew Wilcox (Oracle) 
Signed-off-by: Andrew Morton 
Reviewed-by: Dave Chinner 
Reviewed-by: John Hubbard 
Reviewed-by: Christoph Hellwig 
Reviewed-by: William Kucharski 
Cc: Chao Yu 
Cc: Cong Wang 
Cc: Darrick J. Wong 
Cc: Eric Biggers 
Cc: Gao Xiang 
Cc: Jaegeuk Kim 
Cc: Joseph Qi 
Cc: Junxiao Bi 
Cc: Michal Hocko 
Cc: Zi Yan 
Cc: Johannes Thumshirn 
Cc: Miklos Szeredi 
Link: http://lkml.kernel.org/r/20200414150233.24495-3-willy@infradead.org
Signed-off-by: Linus Torvalds

mm: move readahead prototypes from mm.h

2020-06-02T17:59:06+00:00

Patch series "Change readahead API", v11.

This series adds a readahead address_space operation to replace the
readpages operation.  The key difference is that pages are added to the
page cache as they are allocated (and then looked up by the filesystem)
instead of passing them on a list to the readpages operation and having
the filesystem add them to the page cache.  It's a net reduction in code
for each implementation, more efficient than walking a list, and solves
the direct-write vs buffered-read problem reported by yu kuai at
http://lkml.kernel.org/r/20200116063601.39201-1-yukuai3@huawei.com

The only unconverted filesystems are those which use fscache.  Their
conversion is pending Dave Howells' rewrite which will make the
conversion substantially easier.  This should be completed by the end of
the year.

I want to thank the reviewers/testers; Dave Chinner, John Hubbard, Eric
Biggers, Johannes Thumshirn, Dave Sterba, Zi Yan, Christoph Hellwig and
Miklos Szeredi have done a marvellous job of providing constructive
criticism.

These patches pass an xfstests run on ext4, xfs & btrfs with no
regressions that I can tell (some of the tests seem a little flaky
before and remain flaky afterwards).

This patch (of 25):

The readahead code is part of the page cache so should be found in the
pagemap.h file.  force_page_cache_readahead is only used within mm, so
move it to mm/internal.h instead.  Remove the parameter names where they
add no value, and rename the ones which were actively misleading.

Signed-off-by: Matthew Wilcox (Oracle) 
Signed-off-by: Andrew Morton 
Reviewed-by: John Hubbard 
Reviewed-by: Christoph Hellwig 
Reviewed-by: William Kucharski 
Reviewed-by: Johannes Thumshirn 
Cc: Chao Yu 
Cc: Cong Wang 
Cc: Darrick J. Wong 
Cc: Dave Chinner 
Cc: Eric Biggers 
Cc: Gao Xiang 
Cc: Jaegeuk Kim 
Cc: Joseph Qi 
Cc: Junxiao Bi 
Cc: Michal Hocko 
Cc: Zi Yan 
Cc: Miklos Szeredi 
Link: http://lkml.kernel.org/r/20200414150233.24495-1-willy@infradead.org
Link: http://lkml.kernel.org/r/20200414150233.24495-2-willy@infradead.org
Signed-off-by: Linus Torvalds

fs: Export generic_fadvise()

2019-08-31T05:43:58+00:00

Filesystems will need to call this function from their fadvise handlers.

CC: stable@vger.kernel.org
Reviewed-by: Darrick J. Wong 
Signed-off-by: Jan Kara 
Signed-off-by: Darrick J. Wong

vfs: implement readahead(2) using POSIX_FADV_WILLNEED

2018-08-30T18:01:32+00:00

The implementation of readahead(2) syscall is identical to that of
fadvise64(POSIX_FADV_WILLNEED) with a few exceptions:
1. readahead(2) returns -EINVAL for !mapping->a_ops and fadvise64()
   ignores the request and returns 0.
2. fadvise64() checks for integer overflow corner case
3. fadvise64() calls the optional filesystem fadvise() file operation

Unite the two implementations by calling vfs_fadvise() from readahead(2)
syscall. Check the !mapping->a_ops in readahead(2) syscall to preserve
documented syscall ABI behaviour.

Suggested-by: Miklos Szeredi 
Fixes: d1d04ef8572b ("ovl: stack file ops")
Signed-off-by: Amir Goldstein 
Signed-off-by: Miklos Szeredi

vfs: add the fadvise() file operation

2018-08-30T15:08:35+00:00

This is going to be used by overlayfs and possibly useful
for other filesystems.

Signed-off-by: Amir Goldstein 
Signed-off-by: Miklos Szeredi

mm/fadvise.c: fix signed overflow UBSAN complaint

2018-08-17T23:20:30+00:00

Signed integer overflow is undefined according to the C standard.  The
overflow in ksys_fadvise64_64() is deliberate, but since it is signed
overflow, UBSAN complains:

	UBSAN: Undefined behaviour in mm/fadvise.c:76:10
	signed integer overflow:
	4 + 9223372036854775805 cannot be represented in type 'long long int'

Use unsigned types to do math.  Unsigned overflow is defined so UBSAN
will not complain about it.  This patch doesn't change generated code.

[akpm@linux-foundation.org: add comment explaining the casts]
Link: http://lkml.kernel.org/r/20180629184453.7614-1-aryabinin@virtuozzo.com
Signed-off-by: Andrey Ryabinin 
Reported-by: 
Reviewed-by: Andrew Morton 
Cc: Alexander Potapenko 
Cc: Dmitry Vyukov 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: add ksys_fadvise64_64() helper; remove in-kernel call to sys_fadvise64_64()

2018-04-02T18:16:10+00:00

Using the ksys_fadvise64_64() helper allows us to avoid the in-kernel
calls to the sys_fadvise64_64() syscall. The ksys_ prefix denotes that
this function is meant as a drop-in replacement for the syscall. In
particular, it uses the same calling convention as ksys_fadvise64_64().

Some compat stubs called sys_fadvise64(), which then just passed through
the arguments to sys_fadvise64_64(). Get rid of this indirection, and call
ksys_fadvise64_64() directly.

This patch is part of a series which removes in-kernel calls to syscalls.
On this basis, the syscall entry path can be streamlined. For details, see
http://lkml.kernel.org/r/20180325162527.GA17492@light.dominikbrodowski.net

Cc: Andrew Morton 
Cc: linux-mm@kvack.org
Signed-off-by: Dominik Brodowski

mm/fadvise: discard partial page if endbyte is also EOF

2018-02-01T01:18:39+00:00

During our recent testing with fadvise(FADV_DONTNEED), we find that if
given offset/length is not page-aligned, the last page will not be
discarded.  The tool we use is vmtouch (https://hoytech.com/vmtouch/),
we map a 10KB-sized file into memory and then try to run this tool to
evict the whole file mapping, but the last single page always remains
staying in the memory:

$./vmtouch -e test_10K
           Files: 1
     Directories: 0
   Evicted Pages: 3 (12K)
         Elapsed: 2.1e-05 seconds

$./vmtouch test_10K
           Files: 1
     Directories: 0
  Resident Pages: 1/3  4K/12K  33.3%
         Elapsed: 5.5e-05 seconds

However when we test with an older kernel, say 3.10, this problem is
gone.  So we wonder if this is a regression:

$./vmtouch -e test_10K
           Files: 1
     Directories: 0
   Evicted Pages: 3 (12K)
         Elapsed: 8.2e-05 seconds

$./vmtouch test_10K
           Files: 1
     Directories: 0
  Resident Pages: 0/3  0/12K  0%  <-- partial page also discarded
         Elapsed: 5e-05 seconds

After digging a little bit into this problem, we find it seems not a
regression.  Not discarding partial page is likely to be on purpose
according to commit 441c228f817f ("mm: fadvise: document the
fadvise(FADV_DONTNEED) behaviour for partial pages") written by Mel
Gorman.  He explained why partial pages should be preserved instead of
being discarded when using fadvise(FADV_DONTNEED).

However, the interesting part is that the actual code did NOT work as
the same as it was described, the partial page was still discarded
anyway, due to a calculation mistake of `end_index' passed to
invalidate_mapping_pages().  This mistake has not been fixed until
recently, that's why we fail to reproduce our problem in old kernels.
The fix is done in commit 18aba41cbf ("mm/fadvise.c: do not discard
partial pages with POSIX_FADV_DONTNEED") by Oleg Drokin.

Back to the original testing, our problem becomes that there is a
special case that, if the page-unaligned `endbyte' is also the end of
file, it is not necessary at all to preserve the last partial page, as
we all know no one else will use the rest of it.  It should be safe
enough if we just discard the whole page.  So we add an EOF check in
this patch.

We also find a poosbile real world issue in mainline kernel.  Assume
such scenario: A userspace backup application want to backup a huge
amount of small files (<4k) at once, the developer might (I guess) want
to use fadvise(FADV_DONTNEED) to save memory.  However, FADV_DONTNEED
won't really happen since the only page mapped is a partial page, and
kernel will preserve it.  Our patch also fixes this problem, since we
know the endbyte is EOF, so we discard it.

Here is a simple reproducer to reproduce and verify each scenario we
described above:

  test_fadvise.c
  ==============================
  #include 
  #include 
  #include 
  #include 
  #include 
  #include 
  #include 

  int main(int argc, char **argv)
  {
  	int i, fd, ret, len;
  	struct stat buf;
  	void *addr;
  	unsigned char *vec;
  	char *strbuf;
  	ssize_t pagesize = getpagesize();
  	ssize_t filesize;

  	fd = open(argv[1], O_RDWR|O_CREAT, S_IRUSR|S_IWUSR);
  	if (fd < 0)
  		return -1;
  	filesize = strtoul(argv[2], NULL, 10);

  	strbuf = malloc(filesize);
  	memset(strbuf, 42, filesize);
  	write(fd, strbuf, filesize);
  	free(strbuf);
  	fsync(fd);

  	len = (filesize + pagesize - 1) / pagesize;
  	printf("length of pages: %d\n", len);

  	addr = mmap(NULL, filesize, PROT_READ, MAP_SHARED, fd, 0);
  	if (addr == MAP_FAILED)
  		return -1;

  	ret = posix_fadvise(fd, 0, filesize, POSIX_FADV_DONTNEED);
  	if (ret < 0)
  		return -1;

  	vec = malloc(len);
  	ret = mincore(addr, filesize, (void *)vec);
  	if (ret < 0)
  		return -1;

  	for (i = 0; i < len; i++)
  		printf("pages[%d]: %x\n", i, vec[i] & 0x1);

  	free(vec);
  	close(fd);

  	return 0;
  }
  ==============================

Test 1: running on kernel with commit 18aba41cbf reverted:

  [root@caspar ~]# uname -r
  4.15.0-rc6.revert+
  [root@caspar ~]# ./test_fadvise file1 1024
  length of pages: 1
  pages[0]: 0    # <-- partial page discarded
  [root@caspar ~]# ./test_fadvise file2 8192
  length of pages: 2
  pages[0]: 0
  pages[1]: 0
  [root@caspar ~]# ./test_fadvise file3 10240
  length of pages: 3
  pages[0]: 0
  pages[1]: 0
  pages[2]: 0    # <-- partial page discarded

Test 2: running on mainline kernel:

  [root@caspar ~]# uname -r
  4.15.0-rc6+
  [root@caspar ~]# ./test_fadvise test1 1024
  length of pages: 1
  pages[0]: 1    # <-- partial and the only page not discarded
  [root@caspar ~]# ./test_fadvise test2 8192
  length of pages: 2
  pages[0]: 0
  pages[1]: 0
  [root@caspar ~]# ./test_fadvise test3 10240
  length of pages: 3
  pages[0]: 0
  pages[1]: 0
  pages[2]: 1    # <-- partial page not discarded

Test 3: running on kernel with this patch:

  [root@caspar ~]# uname -r
  4.15.0-rc6.patched+
  [root@caspar ~]# ./test_fadvise test1 1024
  length of pages: 1
  pages[0]: 0    # <-- partial page and EOF, discarded
  [root@caspar ~]# ./test_fadvise test2 8192
  length of pages: 2
  pages[0]: 0
  pages[1]: 0
  [root@caspar ~]# ./test_fadvise test3 10240
  length of pages: 3
  pages[0]: 0
  pages[1]: 0
  pages[2]: 0    # <-- partial page and EOF, discarded

[akpm@linux-foundation.org: tweak code comment]
Link: http://lkml.kernel.org/r/5222da9ee20e1695eaabb69f631f200d6e6b8876.1515132470.git.jinli.zjl@alibaba-inc.com
Signed-off-by: shidao.ytt 
Signed-off-by: Caspar Zhang 
Reviewed-by: Oliver Yang 
Cc: Mel Gorman 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

License cleanup: add SPDX GPL-2.0 license identifier to files with no license

2017-11-02T10:10:55+00:00

Many source files in the tree are missing licensing information, which
makes it harder for compliance tools to determine the correct license.

By default all files without license information are under the default
license of the kernel, which is GPL version 2.

Update the files which contain no license information with the 'GPL-2.0'
SPDX license identifier.  The SPDX identifier is a legally binding
shorthand, which can be used instead of the full boiler plate text.

This patch is based on work done by Thomas Gleixner and Kate Stewart and
Philippe Ombredanne.

How this work was done:

Patches were generated and checked against linux-4.14-rc6 for a subset of
the use cases:
 - file had no licensing information it it.
 - file was a */uapi/* one with no licensing information in it,
 - file was a */uapi/* one with existing licensing information,

Further patches will be generated in subsequent months to fix up cases
where non-standard license headers were used, and references to license
had to be inferred by heuristics based on keywords.

The analysis to determine which SPDX License Identifier to be applied to
a file was done in a spreadsheet of side by side results from of the
output of two independent scanners (ScanCode & Windriver) producing SPDX
tag:value files created by Philippe Ombredanne.  Philippe prepared the
base worksheet, and did an initial spot review of a few 1000 files.

The 4.13 kernel was the starting point of the analysis with 60,537 files
assessed.  Kate Stewart did a file by file comparison of the scanner
results in the spreadsheet to determine which SPDX license identifier(s)
to be applied to the file. She confirmed any determination that was not
immediately clear with lawyers working with the Linux Foundation.

Criteria used to select files for SPDX license identifier tagging was:
 - Files considered eligible had to be source code files.
 - Make and config files were included as candidates if they contained >5
   lines of source
 - File already had some variant of a license header in it (even if <5
   lines).

All documentation files were explicitly excluded.

The following heuristics were used to determine which SPDX license
identifiers to apply.

 - when both scanners couldn't find any license traces, file was
   considered to have no license information in it, and the top level
   COPYING file license applied.

   For non */uapi/* files that summary was:

   SPDX license identifier                            # files
   ---------------------------------------------------|-------
   GPL-2.0                                              11139

   and resulted in the first patch in this series.

   If that file was a */uapi/* path one, it was "GPL-2.0 WITH
   Linux-syscall-note" otherwise it was "GPL-2.0".  Results of that was:

   SPDX license identifier                            # files
   ---------------------------------------------------|-------
   GPL-2.0 WITH Linux-syscall-note                        930

   and resulted in the second patch in this series.

 - if a file had some form of licensing information in it, and was one
   of the */uapi/* ones, it was denoted with the Linux-syscall-note if
   any GPL family license was found in the file or had no licensing in
   it (per prior point).  Results summary:

   SPDX license identifier                            # files
   ---------------------------------------------------|------
   GPL-2.0 WITH Linux-syscall-note                       270
   GPL-2.0+ WITH Linux-syscall-note                      169
   ((GPL-2.0 WITH Linux-syscall-note) OR BSD-2-Clause)    21
   ((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause)    17
   LGPL-2.1+ WITH Linux-syscall-note                      15
   GPL-1.0+ WITH Linux-syscall-note                       14
   ((GPL-2.0+ WITH Linux-syscall-note) OR BSD-3-Clause)    5
   LGPL-2.0+ WITH Linux-syscall-note                       4
   LGPL-2.1 WITH Linux-syscall-note                        3
   ((GPL-2.0 WITH Linux-syscall-note) OR MIT)              3
   ((GPL-2.0 WITH Linux-syscall-note) AND MIT)             1

   and that resulted in the third patch in this series.

 - when the two scanners agreed on the detected license(s), that became
   the concluded license(s).

 - when there was disagreement between the two scanners (one detected a
   license but the other didn't, or they both detected different
   licenses) a manual inspection of the file occurred.

 - In most cases a manual inspection of the information in the file
   resulted in a clear resolution of the license that should apply (and
   which scanner probably needed to revisit its heuristics).

 - When it was not immediately clear, the license identifier was
   confirmed with lawyers working with the Linux Foundation.

 - If there was any question as to the appropriate license identifier,
   the file was flagged for further research and to be revisited later
   in time.

In total, over 70 hours of logged manual review was done on the
spreadsheet to determine the SPDX license identifiers to apply to the
source files by Kate, Philippe, Thomas and, in some cases, confirmation
by lawyers working with the Linux Foundation.

Kate also obtained a third independent scan of the 4.13 code base from
FOSSology, and compared selected files where the other two scanners
disagreed against that SPDX file, to see if there was new insights.  The
Windriver scanner is based on an older version of FOSSology in part, so
they are related.

Thomas did random spot checks in about 500 files from the spreadsheets
for the uapi headers and agreed with SPDX license identifier in the
files he inspected. For the non-uapi files Thomas did random spot checks
in about 15000 files.

In initial set of patches against 4.14-rc6, 3 files were found to have
copy/paste license identifier errors, and have been fixed to reflect the
correct identifier.

Additionally Philippe spent 10 hours this week doing a detailed manual
inspection and review of the 12,461 patched files from the initial patch
version early this week with:
 - a full scancode scan run, collecting the matched texts, detected
   license ids and scores
 - reviewing anything where there was a license detected (about 500+
   files) to ensure that the applied SPDX license was correct
 - reviewing anything where there was no detection but the patch license
   was not GPL-2.0 WITH Linux-syscall-note to ensure that the applied
   SPDX license was correct

This produced a worksheet with 20 files needing minor correction.  This
worksheet was then exported into 3 different .csv files for the
different types of files to be modified.

These .csv files were then reviewed by Greg.  Thomas wrote a script to
parse the csv files and add the proper SPDX tag to the file, in the
format that the file expected.  This script was further refined by Greg
based on the output to detect more types of files automatically and to
distinguish between header and source .c files (which need different
comment types.)  Finally Greg ran the script using the .csv files to
generate the patches.

Reviewed-by: Kate Stewart 
Reviewed-by: Philippe Ombredanne 
Reviewed-by: Thomas Gleixner 
Signed-off-by: Greg Kroah-Hartman