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0fe2735d5e
calculate_order() currently has two nested loops. The inner one that gradually modifies the acceptable waste from 1/16 up to 1/4, and the outer one that decreases min_objects down to 2. Upon closer inspection, the outer loop is unnecessary. Decreasing min_objects could have in theory two effects to make the inner loop and its call to calc_slab_order() succeed where a previous iteration with higher min_objects would not: - it could cause the min_objects-derived min_order to fit within slub_max_order. But min_objects is already pre-capped to max_objects that's derived from slub_max_order above the loops, so every iteration tries at least slub_max_order in calc_slab_order() - it could cause calc_slab_order() to be called with lower min_objects thus potentially lower min_order in its loop. This would make a difference if the lower order could cause the fractional waste test to succeed where a higher order has already failed with same fract_leftover in the previous iteration with a higher min_order. But that's not possible, because increasing the order can only result in lower (or same) fractional waste. If we increase the slab size 2 times, we will fit at least 2 times the number of objects (thus same fraction of waste), or it will allow us to fit one more object (lower fraction of waste). For more confidence I have tried adding a printk to notify when decreasing min_objects resulted in a success, and simulated calculations for a range of object sizes, nr_cpus and page_sizes. As expected, the printk never triggered. Thus remove the outer loop and adjust comments accordingly. There's almost no functional change except a weird corner case when slub_min_objects=1 on boot command line would cause the whole two nested loops to be skipped before this patch. Now it would try to find the best layout as usual, resulting in potentially higher orderthat minimizes waste. This is not wrong and will be further expanded by the next patch. Signed-off-by: Vlastimil Babka <vbabka@suse.cz> Reviewed-by: Feng Tang <feng.tang@intel.com> Reviewed-and-tested-by: Jay Patel <jaypatel@linux.ibm.com> |
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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 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.