user/sven/linux.git/Documentation/blockdev, branch v5.1.15

zram: idle writeback fixes and cleanup

2019-01-09T01:15:10Z

This patch includes some fixes and cleanup for idle-page writeback. 1. writeback_limit interface Now writeback_limit interface is rather conusing. For example, once writeback limit budget is exausted, admin can see 0 from /sys/block/zramX/writeback_limit which is same semantic with disable writeback_limit at this moment. IOW, admin cannot tell that zero came from disable writeback limit or exausted writeback limit. To make the interface clear, let's sepatate enable of writeback limit to another knob - /sys/block/zram0/writeback_limit_enable * before: while true : # to re-enable writeback limit once previous one is used up echo 0 > /sys/block/zram0/writeback_limit echo $((200<<20)) > /sys/block/zram0/writeback_limit .. .. # used up the writeback limit budget * new # To enable writeback limit, from the beginning, admin should # enable it. echo $((200<<20)) > /sys/block/zram0/writeback_limit echo 1 > /sys/block/zram/0/writeback_limit_enable while true : echo $((200<<20)) > /sys/block/zram0/writeback_limit .. .. # used up the writeback limit budget It's much strightforward. 2. fix condition check idle/huge writeback mode check The mode in writeback_store is not bit opeartion any more so no need to use bit operations. Furthermore, current condition check is broken in that it does writeback every pages regardless of huge/idle. 3. clean up idle_store No need to use goto. [minchan@kernel.org: missed spin_lock_init] Link: http://lkml.kernel.org/r/20190103001601.GA255139@google.com Link: http://lkml.kernel.org/r/20181224033529.19450-1-minchan@kernel.org Signed-off-by: Minchan Kim Suggested-by: John Dias Cc: Sergey Senozhatsky Cc: John Dias Cc: Srinivas Paladugu Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

zram: writeback throttle

2018-12-28T20:11:49Z

If there are lots of write IO with flash device, it could have a wearout problem of storage. To overcome the problem, admin needs to design write limitation to guarantee flash health for entire product life. This patch creates a new knob "writeback_limit" for zram. writeback_limit's default value is 0 so that it doesn't limit any writeback. If admin want to measure writeback count in a certain period, he could know it via /sys/block/zram0/bd_stat's 3rd column. If admin want to limit writeback as per-day 400M, he could do it like below. MB_SHIFT=20 4K_SHIFT=12 echo $((400<>4K_SHIFT)) > \ /sys/block/zram0/writeback_limit. If admin want to allow further write again, he could do it like below echo 0 > /sys/block/zram0/writeback_limit If admin want to see remaining writeback budget, cat /sys/block/zram0/writeback_limit The writeback_limit count will reset whenever you reset zram (e.g., system reboot, echo 1 > /sys/block/zramX/reset) so keeping how many of writeback happened until you reset the zram to allocate extra writeback budget in next setting is user's job. [minchan@kernel.org: v4] Link: http://lkml.kernel.org/r/20181203024045.153534-8-minchan@kernel.org Link: http://lkml.kernel.org/r/20181127055429.251614-8-minchan@kernel.org Signed-off-by: Minchan Kim Reviewed-by: Sergey Senozhatsky Cc: Joey Pabalinas Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

zram: add bd_stat statistics

2018-12-28T20:11:49Z

bd_stat represents things that happened in the backing device. Currently it supports bd_counts, bd_reads and bd_writes which are helpful to understand wearout of flash and memory saving. [minchan@kernel.org: v4] Link: http://lkml.kernel.org/r/20181203024045.153534-7-minchan@kernel.org Link: http://lkml.kernel.org/r/20181127055429.251614-7-minchan@kernel.org Signed-off-by: Minchan Kim Reviewed-by: Sergey Senozhatsky Cc: Joey Pabalinas Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

zram: support idle/huge page writeback

2018-12-28T20:11:49Z

Add a new feature "zram idle/huge page writeback". In the zram-swap use case, zram usually has many idle/huge swap pages. It's pointless to keep them in memory (ie, zram). To solve this problem, this feature introduces idle/huge page writeback to the backing device so the goal is to save more memory space on embedded systems. Normal sequence to use idle/huge page writeback feature is as follows, while (1) { # mark allocated zram slot to idle echo all > /sys/block/zram0/idle # leave system working for several hours # Unless there is no access for some blocks on zram, # they are still IDLE marked pages. echo "idle" > /sys/block/zram0/writeback or/and echo "huge" > /sys/block/zram0/writeback # write the IDLE or/and huge marked slot into backing device # and free the memory. } Per the discussion at https://lore.kernel.org/lkml/20181122065926.GG3441@jagdpanzerIV/T/#u, This patch removes direct incommpressibe page writeback feature (d2afd25114f4 ("zram: write incompressible pages to backing device")). Below concerns from Sergey: == &< == "IDLE writeback" is superior to "incompressible writeback". "incompressible writeback" is completely unpredictable and uncontrollable; it depens on data patterns and compression algorithms. While "IDLE writeback" is predictable. I even suspect, that, *ideally*, we can remove "incompressible writeback". "IDLE pages" is a super set which also includes "incompressible" pages. So, technically, we still can do "incompressible writeback" from "IDLE writeback" path; but a much more reasonable one, based on a page idling period. I understand that you want to keep "direct incompressible writeback" around. ZRAM is especially popular on devices which do suffer from flash wearout, so I can see "incompressible writeback" path becoming a dead code, long term. == &< == Below concerns from Minchan: == &< == My concern is if we enable CONFIG_ZRAM_WRITEBACK in this implementation, both hugepage/idlepage writeck will turn on. However someuser want to enable only idlepage writeback so we need to introduce turn on/off knob for hugepage or new CONFIG_ZRAM_IDLEPAGE_WRITEBACK for those usecase. I don't want to make it complicated *if possible*. Long term, I imagine we need to make VM aware of new swap hierarchy a little bit different with as-is. For example, first high priority swap can return -EIO or -ENOCOMP, swap try to fallback to next lower priority swap device. With that, hugepage writeback will work tranparently. So we could regard it as regression because incompressible pages doesn't go to backing storage automatically. Instead, user should do it via "echo huge" > /sys/block/zram/writeback" manually. == &< == Link: http://lkml.kernel.org/r/20181127055429.251614-6-minchan@kernel.org Signed-off-by: Minchan Kim Reviewed-by: Joey Pabalinas Reviewed-by: Sergey Senozhatsky Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

zram: introduce ZRAM_IDLE flag

2018-12-28T20:11:49Z

To support idle page writeback with upcoming patches, this patch introduces a new ZRAM_IDLE flag. Userspace can mark zram slots as "idle" via "echo all > /sys/block/zramX/idle" which marks every allocated zram slot as ZRAM_IDLE. User could see it by /sys/kernel/debug/zram/zram0/block_state. 300 75.033841 ...i 301 63.806904 s..i 302 63.806919 ..hi Once there is IO for the slot, the mark will be disappeared. 300 75.033841 ... 301 63.806904 s..i 302 63.806919 ..hi Therefore, 300th block is idle zpage. With this feature, user can how many zram has idle pages which are waste of memory. Link: http://lkml.kernel.org/r/20181127055429.251614-5-minchan@kernel.org Signed-off-by: Minchan Kim Reviewed-by: Sergey Senozhatsky Reviewed-by: Joey Pabalinas Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

Merge tag 'docs-4.20' of git://git.lwn.net/linux

2018-10-24T17:01:11Z

Pull documentation updates from Jonathan Corbet: "This is a fairly typical cycle for documentation. There's some welcome readability improvements for the formatted output, some LICENSES updates including the addition of the ISC license, the removal of the unloved and unmaintained 00-INDEX files, the deprecated APIs document from Kees, more MM docs from Mike Rapoport, and the usual pile of typo fixes and corrections" * tag 'docs-4.20' of git://git.lwn.net/linux: (41 commits) docs: Fix typos in histogram.rst docs: Introduce deprecated APIs list kernel-doc: fix declaration type determination doc: fix a typo in adding-syscalls.rst docs/admin-guide: memory-hotplug: remove table of contents doc: printk-formats: Remove bogus kobject references for device nodes Documentation: preempt-locking: Use better example dm flakey: Document "error_writes" feature docs/completion.txt: Fix a couple of punctuation nits LICENSES: Add ISC license text LICENSES: Add note to CDDL-1.0 license that it should not be used docs/core-api: memory-hotplug: add some details about locking internals docs/core-api: rename memory-hotplug-notifier to memory-hotplug docs: improve readability for people with poorer eyesight yama: clarify ptrace_scope=2 in Yama documentation docs/vm: split memory hotplug notifier description to Documentation/core-api docs: move memory hotplug description into admin-guide/mm doc: Fix acronym "FEKEK" in ecryptfs docs: fix some broken documentation references iommu: Fix passthrough option documentation ...

drivers/block: Remove DAC960 driver

2018-10-17T15:42:30Z

The DAC960 driver has been obsoleted by the myrb/myrs drivers, so it can be dropped. Signed-off-by: Hannes Reinecke Reviewed-by: Christoph Hellwig Signed-off-by: Jens Axboe

block: Finish renaming REQ_DISCARD into REQ_OP_DISCARD

2018-10-03T22:12:28Z

Some time ago REQ_DISCARD was renamed into REQ_OP_DISCARD. Some comments and documentation files were not updated however. Update these comments and documentation files. See also commit 4e1b2d52a80d ("block, fs, drivers: remove REQ_OP compat defs and related code"). Signed-off-by: Bart Van Assche Cc: Mike Christie Cc: Martin K. Petersen Cc: Philipp Reisner Cc: Lars Ellenberg Signed-off-by: Jens Axboe

Drop all 00-INDEX files from Documentation/

2018-09-09T21:08:58Z

This is a respin with a wider audience (all that get_maintainer returned) and I know this spams a *lot* of people. Not sure what would be the correct way, so my apologies for ruining your inbox. The 00-INDEX files are supposed to give a summary of all files present in a directory, but these files are horribly out of date and their usefulness is brought into question. Often a simple "ls" would reveal the same information as the filenames are generally quite descriptive as a short introduction to what the file covers (it should not surprise anyone what Documentation/sched/sched-design-CFS.txt covers) A few years back it was mentioned that these files were no longer really needed, and they have since then grown further out of date, so perhaps it is time to just throw them out. A short status yields the following _outdated_ 00-INDEX files, first counter is files listed in 00-INDEX but missing in the directory, last is files present but not listed in 00-INDEX. List of outdated 00-INDEX: Documentation: (4/10) Documentation/sysctl: (0/1) Documentation/timers: (1/0) Documentation/blockdev: (3/1) Documentation/w1/slaves: (0/1) Documentation/locking: (0/1) Documentation/devicetree: (0/5) Documentation/power: (1/1) Documentation/powerpc: (0/5) Documentation/arm: (1/0) Documentation/x86: (0/9) Documentation/x86/x86_64: (1/1) Documentation/scsi: (4/4) Documentation/filesystems: (2/9) Documentation/filesystems/nfs: (0/2) Documentation/cgroup-v1: (0/2) Documentation/kbuild: (0/4) Documentation/spi: (1/0) Documentation/virtual/kvm: (1/0) Documentation/scheduler: (0/2) Documentation/fb: (0/1) Documentation/block: (0/1) Documentation/networking: (6/37) Documentation/vm: (1/3) Then there are 364 subdirectories in Documentation/ with several files that are missing 00-INDEX alltogether (and another 120 with a single file and no 00-INDEX). I don't really have an opinion to whether or not we /should/ have 00-INDEX, but the above 00-INDEX should either be removed or be kept up to date. If we should keep the files, I can try to keep them updated, but I rather not if we just want to delete them anyway. As a starting point, remove all index-files and references to 00-INDEX and see where the discussion is going. Signed-off-by: Henrik Austad Acked-by: "Paul E. McKenney" Just-do-it-by: Steven Rostedt Reviewed-by: Jens Axboe Acked-by: Paul Moore Acked-by: Greg Kroah-Hartman Acked-by: Mark Brown Acked-by: Mike Rapoport Cc: [Almost everybody else] Signed-off-by: Jonathan Corbet

zram: introduce zram memory tracking

2018-06-08T00:34:34Z

zRam as swap is useful for small memory device. However, swap means those pages on zram are mostly cold pages due to VM's LRU algorithm. Especially, once init data for application are touched for launching, they tend to be not accessed any more and finally swapped out. zRAM can store such cold pages as compressed form but it's pointless to keep in memory. Better idea is app developers free them directly rather than remaining them on heap. This patch tell us last access time of each block of zram via "cat /sys/kernel/debug/zram/zram0/block_state". The output is as follows, 300 75.033841 .wh 301 63.806904 s.. 302 63.806919 ..h First column is zram's block index and 3rh one represents symbol (s: same page w: written page to backing store h: huge page) of the block state. Second column represents usec time unit of the block was last accessed. So above example means the 300th block is accessed at 75.033851 second and it was huge so it was written to the backing store. Admin can leverage this information to catch cold|incompressible pages of process with *pagemap* once part of heaps are swapped out. I used the feature a few years ago to find memory hoggers in userspace to notify them what memory they have wasted without touch for a long time. With it, they could reduce unnecessary memory space. However, at that time, I hacked up zram for the feature but now I need the feature again so I decided it would be better to upstream rather than keeping it alone. I hope I submit the userspace tool to use the feature soon. [akpm@linux-foundation.org: fix i386 printk warning] [minchan@kernel.org: use ktime_get_boottime() instead of sched_clock()] Link: http://lkml.kernel.org/r/20180420063525.GA253739@rodete-desktop-imager.corp.google.com [akpm@linux-foundation.org: documentation tweak] [akpm@linux-foundation.org: fix i386 printk warning] [minchan@kernel.org: fix compile warning] Link: http://lkml.kernel.org/r/20180508104849.GA8209@rodete-desktop-imager.corp.google.com [rdunlap@infradead.org: fix printk formats] Link: http://lkml.kernel.org/r/3652ccb1-96ef-0b0b-05d1-f661d7733dcc@infradead.org Link: http://lkml.kernel.org/r/20180416090946.63057-5-minchan@kernel.org Signed-off-by: Minchan Kim Signed-off-by: Randy Dunlap Reviewed-by: Sergey Senozhatsky Acked-by: Greg Kroah-Hartman Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds