70704c33db
Until now, DM bufio's waiting for IO from reclaim context in its shrinker has caused kswapd to block; which results in systemic IO stalls and even deadlock, e.g.: https://www.redhat.com/archives/dm-devel/2020-March/msg00025.html Here is Dave Chinner's problem description that motivated this fix, from: https://lore.kernel.org/linux-fsdevel/20190809215733.GZ7777@dread.disaster.area/ "Waiting for IO in kswapd reclaim context is considered harmful - kswapd context shrinker reclaim should be as non-blocking as possible, and any back-off to wait for IO to complete should be done by the high level reclaim core once it's completed an entire reclaim scan cycle of everything.... What follows from that, and is pertinent in this situation, is that if you don't block kswapd, then other reclaim contexts are not going to get stuck waiting for it regardless of the reclaim context they use." Continued elsewhere: "The only way to fix this problem once and for all is to stop using the shrinker as a mechanism to issue and wait on IO. If you need background writeback of dirty buffers, do it from a WQ_MEM_RECLAIM workqueue that isn't directly in the memory reclaim path and so can issue writeback and block safely from a GFP_KERNEL context. Kick the workqueue from the shrinker context, but get rid of the IO submission and waiting from the shrinker and all the GFP_NOFS memory reclaim recursion problems go away." As such, this commit moves buffer cleanup to a workqueue. Suggested-by: Dave Chinner <dchinner@redhat.com> Reported-by: Tahsin Erdogan <tahsin@google.com> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Tested-by: Gabriel Krisman Bertazi <krisman@collabora.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> |
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| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.