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05356938a4
If there are extreme heavy write I/O continuously hit on relative small cache device (512GB in my testing), it is possible to make counter c->gc_stats.in_use continue to increase and exceed CUTOFF_CACHE_ADD. If 'c->gc_stats.in_use > CUTOFF_CACHE_ADD' happens, all following write requests will bypass the cache device because check_should_bypass() returns 'true'. Because all writes bypass the cache device, counter c->sectors_to_gc has no chance to be negative value, and garbage collection thread won't be waken up even the whole cache becomes clean after writeback accomplished. The aftermath is that all write I/Os go directly into backing device even the cache device is clean. To avoid the above situation, this patch uses a quite conservative way to fix: if 'c->gc_stats.in_use > CUTOFF_CACHE_ADD' happens, only wakes up garbage collection thread when the whole cache device is clean. Before the fix, the writes-always-bypass situation happens after 10+ hours write I/O pressure on 512GB Intel optane memory which acts as cache device. After this fix, such situation doesn't happen after 36+ hours testing. Signed-off-by: Coly Li <colyli@suse.de> Link: https://lore.kernel.org/r/20240528120914.28705-3-colyli@suse.de Signed-off-by: Jens Axboe <axboe@kernel.dk> |
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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 reStructuredText 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.