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To no surprise (since we've flip-flopped over the use of PIN_HIGH a few times), doing a search by address over a pathologically fragmented address space is exceeding slow. To protect ourselves from nearly unbounded latency (think searching a million holes while under struct_mutex), limit the search for the highest available hole and fallback to best-fit if it fails. In the pathologically fragmented case, such as igt/gem_ctx_thrash, the effect is dramatic, bringing the runtime down from hours to seconds (depending on how many other slow searches you hit, e.g. alloc_iova() and alloc_vmap_area() both degrade to a slow rbtree walk after their small cache is exhausted). For the real world, the number of search steps is unlikely to be significant as we should only need to search once per new context. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20180521082131.13744-3-chris@chris-wilson.co.uk
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.
See Documentation/00-INDEX for a list of what is contained in each file.
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.