Huan Yang
c87a1268e9
When invoke memfd_pin_folios, we need offer an array to save each folio which we pinned. The current way is dynamic alloc an array(use kvmalloc), get folios, save into udmabuf and then free. Depend on the size, kvmalloc can do something different: Below PAGE_SIZE, slab allocator will be used, which have good alloc performance, due to it cached page. PAGE_SIZE - PCP Order, PCP(per-cpu-pageset) also given buddy page a cache in each CPU, so different CPU no need to hold some lock(zone or some) to get the locally page. If PCP cached page, the access also fast. PAGE_SIZE - BUDDY_MAX, try to get page from buddy, due to kvmalloc adjusted the gfp flags, if zone freelist can't alloc page(fast path), we will not enter slowpath to reclaim memory. Due to need hold lock and check, may slow, but still fast than vmalloc. Anything wrong will fallback into vmalloc to alloc memory, it obtains contiguous virtual addresses by loop alloc order 0 page(PAGE_SIZE), and then map it into vmalloc area. If necessary, page alloc may enter slowpath to reclaim memory. Hence, if fallback into vmalloc, it's slow. When create, we need to iter each udmabuf item, then pin it's range folios, if each item's range folio's count is large, we may fallback each into vmalloc. This patch find the largest range folio in items, then alloc this size's folio array. When pin range folios, reuse this array. Signed-off-by: Huan Yang <link@vivo.com> Acked-by: Vivek Kasireddy <vivek.kasireddy@intel.com> Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20240918025238.2957823-8-link@vivo.com
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.