kernel.git/mm/slob.c, branch linux-5.7.y

mm, sl[aou]b: guarantee natural alignment for kmalloc(power-of-two)

2019-10-07T22:47:20Z

In most configurations, kmalloc() happens to return naturally aligned (i.e. aligned to the block size itself) blocks for power of two sizes. That means some kmalloc() users might unknowingly rely on that alignment, until stuff breaks when the kernel is built with e.g. CONFIG_SLUB_DEBUG or CONFIG_SLOB, and blocks stop being aligned. Then developers have to devise workaround such as own kmem caches with specified alignment [1], which is not always practical, as recently evidenced in [2]. The topic has been discussed at LSF/MM 2019 [3]. Adding a 'kmalloc_aligned()' variant would not help with code unknowingly relying on the implicit alignment. For slab implementations it would either require creating more kmalloc caches, or allocate a larger size and only give back part of it. That would be wasteful, especially with a generic alignment parameter (in contrast with a fixed alignment to size). Ideally we should provide to mm users what they need without difficult workarounds or own reimplementations, so let's make the kmalloc() alignment to size explicitly guaranteed for power-of-two sizes under all configurations. What this means for the three available allocators? * SLAB object layout happens to be mostly unchanged by the patch. The implicitly provided alignment could be compromised with CONFIG_DEBUG_SLAB due to redzoning, however SLAB disables redzoning for caches with alignment larger than unsigned long long. Practically on at least x86 this includes kmalloc caches as they use cache line alignment, which is larger than that. Still, this patch ensures alignment on all arches and cache sizes. * SLUB layout is also unchanged unless redzoning is enabled through CONFIG_SLUB_DEBUG and boot parameter for the particular kmalloc cache. With this patch, explicit alignment is guaranteed with redzoning as well. This will result in more memory being wasted, but that should be acceptable in a debugging scenario. * SLOB has no implicit alignment so this patch adds it explicitly for kmalloc(). The potential downside is increased fragmentation. While pathological allocation scenarios are certainly possible, in my testing, after booting a x86_64 kernel+userspace with virtme, around 16MB memory was consumed by slab pages both before and after the patch, with difference in the noise. [1] https://lore.kernel.org/linux-btrfs/c3157c8e8e0e7588312b40c853f65c02fe6c957a.1566399731.git.christophe.leroy@c-s.fr/ [2] https://lore.kernel.org/linux-fsdevel/20190225040904.5557-1-ming.lei@redhat.com/ [3] https://lwn.net/Articles/787740/ [akpm@linux-foundation.org: documentation fixlet, per Matthew] Link: http://lkml.kernel.org/r/20190826111627.7505-3-vbabka@suse.cz Signed-off-by: Vlastimil Babka Reviewed-by: Matthew Wilcox (Oracle) Acked-by: Michal Hocko Acked-by: Kirill A. Shutemov Acked-by: Christoph Hellwig Cc: David Sterba Cc: Christoph Lameter Cc: Pekka Enberg Cc: David Rientjes Cc: Ming Lei Cc: Dave Chinner Cc: "Darrick J . Wong" Cc: Christoph Hellwig Cc: James Bottomley Cc: Vlastimil Babka Cc: Joonsoo Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm, sl[ou]b: improve memory accounting

2019-10-07T22:47:20Z

Patch series "guarantee natural alignment for kmalloc()", v2. This patch (of 2): SLOB currently doesn't account its pages at all, so in /proc/meminfo the Slab field shows zero. Modifying a counter on page allocation and freeing should be acceptable even for the small system scenarios SLOB is intended for. Since reclaimable caches are not separated in SLOB, account everything as unreclaimable. SLUB currently doesn't account kmalloc() and kmalloc_node() allocations larger than order-1 page, that are passed directly to the page allocator. As they also don't appear in /proc/slabinfo, it might look like a memory leak. For consistency, account them as well. (SLAB doesn't actually use page allocator directly, so no change there). Ideally SLOB and SLUB would be handled in separate patches, but due to the shared kmalloc_order() function and different kfree() implementations, it's easier to patch both at once to prevent inconsistencies. Link: http://lkml.kernel.org/r/20190826111627.7505-2-vbabka@suse.cz Signed-off-by: Vlastimil Babka Cc: Christoph Lameter Cc: Pekka Enberg Cc: David Rientjes Cc: Ming Lei Cc: Dave Chinner Cc: Matthew Wilcox Cc: "Darrick J . Wong" Cc: Christoph Hellwig Cc: James Bottomley Cc: Vlastimil Babka Cc: Joonsoo Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: introduce page_size()

2019-09-24T22:54:08Z

Patch series "Make working with compound pages easier", v2. These three patches add three helpers and convert the appropriate places to use them. This patch (of 3): It's unnecessarily hard to find out the size of a potentially huge page. Replace 'PAGE_SIZE << compound_order(page)' with page_size(page). Link: http://lkml.kernel.org/r/20190721104612.19120-2-willy@infradead.org Signed-off-by: Matthew Wilcox (Oracle) Acked-by: Michal Hocko Reviewed-by: Andrew Morton Reviewed-by: Ira Weiny Acked-by: Kirill A. Shutemov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm/slab: refactor common ksize KASAN logic into slab_common.c

2019-07-12T18:05:42Z

This refactors common code of ksize() between the various allocators into slab_common.c: __ksize() is the allocator-specific implementation without instrumentation, whereas ksize() includes the required KASAN logic. Link: http://lkml.kernel.org/r/20190626142014.141844-5-elver@google.com Signed-off-by: Marco Elver Acked-by: Christoph Lameter Reviewed-by: Andrey Ryabinin Cc: Dmitry Vyukov Cc: Alexander Potapenko Cc: Andrey Konovalov Cc: Pekka Enberg Cc: David Rientjes Cc: Joonsoo Kim Cc: Mark Rutland Cc: Kees Cook Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

slob: use slab_list instead of lru

2019-05-14T16:47:44Z

Currently we use the page->lru list for maintaining lists of slabs. We have a list_head in the page structure (slab_list) that can be used for this purpose. Doing so makes the code cleaner since we are not overloading the lru list. The slab_list is part of a union within the page struct (included here stripped down): union { struct { /* Page cache and anonymous pages */ struct list_head lru; ... }; struct { dma_addr_t dma_addr; }; struct { /* slab, slob and slub */ union { struct list_head slab_list; struct { /* Partial pages */ struct page *next; int pages; /* Nr of pages left */ int pobjects; /* Approximate count */ }; }; ... Here we see that slab_list and lru are the same bits. We can verify that this change is safe to do by examining the object file produced from slob.c before and after this patch is applied. Steps taken to verify: 1. checkout current tip of Linus' tree commit a667cb7a94d4 ("Merge branch 'akpm' (patches from Andrew)") 2. configure and build (select SLOB allocator) CONFIG_SLOB=y CONFIG_SLAB_MERGE_DEFAULT=y 3. dissasemble object file `objdump -dr mm/slub.o > before.s 4. apply patch 5. build 6. dissasemble object file `objdump -dr mm/slub.o > after.s 7. diff before.s after.s Use slab_list list_head instead of the lru list_head for maintaining lists of slabs. Link: http://lkml.kernel.org/r/20190402230545.2929-4-tobin@kernel.org Signed-off-by: Tobin C. Harding Reviewed-by: Roman Gushchin Acked-by: Christoph Lameter Acked-by: Vlastimil Babka Cc: David Rientjes Cc: Joonsoo Kim Cc: Matthew Wilcox Cc: Pekka Enberg Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

slob: respect list_head abstraction layer

2019-05-14T16:47:44Z

Currently we reach inside the list_head. This is a violation of the layer of abstraction provided by the list_head. It makes the code fragile. More importantly it makes the code wicked hard to understand. The code reaches into the list_head structure to counteract the fact that the list _may_ have been changed during slob_page_alloc(). Instead of this we can add a return parameter to slob_page_alloc() to signal that the list was modified (list_del() called with page->lru to remove page from the freelist). This code is concerned with an optimisation that counters the tendency for first fit allocation algorithm to fragment memory into many small chunks at the front of the memory pool. Since the page is only removed from the list when an allocation uses _all_ the remaining memory in the page then in this special case fragmentation does not occur and we therefore do not need the optimisation. Add a return parameter to slob_page_alloc() to signal that the allocation used up the whole page and that the page was removed from the free list. After calling slob_page_alloc() check the return value just added and only attempt optimisation if the page is still on the list. Use list_head API instead of reaching into the list_head structure to check if sp is at the front of the list. Link: http://lkml.kernel.org/r/20190402230545.2929-3-tobin@kernel.org Signed-off-by: Tobin C. Harding Acked-by: Christoph Lameter Acked-by: Vlastimil Babka Cc: David Rientjes Cc: Joonsoo Kim Cc: Matthew Wilcox Cc: Pekka Enberg Cc: Roman Gushchin Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

slab: __GFP_ZERO is incompatible with a constructor

2018-06-08T00:34:34Z

__GFP_ZERO requests that the object be initialised to all-zeroes, while the purpose of a constructor is to initialise an object to a particular pattern. We cannot do both. Add a warning to catch any users who mistakenly pass a __GFP_ZERO flag when allocating a slab with a constructor. Link: http://lkml.kernel.org/r/20180412191322.GA21205@bombadil.infradead.org Fixes: d07dbea46405 ("Slab allocators: support __GFP_ZERO in all allocators") Signed-off-by: Matthew Wilcox Acked-by: Johannes Weiner Acked-by: Vlastimil Babka Acked-by: Michal Hocko Reviewed-by: Andrew Morton Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

slab, slub, slob: add slab_flags_t

2017-11-16T02:21:01Z

Add sparse-checked slab_flags_t for struct kmem_cache::flags (SLAB_POISON, etc). SLAB is bloated temporarily by switching to "unsigned long", but only temporarily. Link: http://lkml.kernel.org/r/20171021100225.GA22428@avx2 Signed-off-by: Alexey Dobriyan Acked-by: Pekka Enberg Cc: Christoph Lameter Cc: David Rientjes Cc: Joonsoo Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm/slob.c: remove an unnecessary check for __GFP_ZERO

2017-11-16T02:21:01Z

Current flow guarantees a valid pointer when handling the __GFP_ZERO case. So remove the unnecessary NULL pointer check. Link: http://lkml.kernel.org/r/1507203141-11959-1-git-send-email-miles.chen@mediatek.com Signed-off-by: Miles Chen Cc: Christoph Lameter Cc: Pekka Enberg Cc: David Rientjes Cc: Joonsoo Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

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

2017-11-02T10:10:55Z

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