Dave Hansen wrote: > > Changes from v2: > - renamed some of the index functions > - added preallocation function > - added flex_array_free_parts() for use with > statically allocated bases > - killed append() function > > Changes from v1: > - to vs too typo > - added __check_part_and_nr() and gave it a warning > - fixed off-by-one check on __nr_part_ptrs() > - added FLEX_ARRAY_INIT() macro > - some kerneldoc comments about the capacity > with various sized objects > - comments to note lack of locking semantice > > -- > > Once a structure goes over PAGE_SIZE*2, we see occasional > allocation failures. Some people have chosen to switch > over to things like vmalloc() that will let them keep > array-like access to such a large structures. But, > vmalloc() has plenty of downsides. > > Here's an alternative. I think it's what Andrew was > suggesting here: > > http://lkml.org/lkml/2009/7/2/518 > > I call it a flexible array. It does all of its work in > PAGE_SIZE bits, so never does an order>0 allocation. > The base level has PAGE_SIZE-2*sizeof(int) bytes of > storage for pointers to the second level. So, with a > 32-bit arch, you get about 4MB (4183112 bytes) of total > storage when the objects pack nicely into a page. It > is half that on 64-bit because the pointers are twice > the size. There's a table detailing this in the code. > > There are kerneldocs for the functions, but here's an > overview: > > flex_array_alloc() - dynamically allocate a base structure > flex_array_free() - free the array and all of the > second-level pages > flex_array_free_parts() - free the second-level pages, but > not the base (for static bases) > flex_array_put() - copy into the array at the given index > flex_array_get() - copy out of the array at the given index > flex_array_prealloc() - preallocate the second-level pages > between the given indexes to > guarantee no allocs will occur at > put() time. Probably premature, but -- I wonder if it's worth adding interfaces to: * copy a range of elements at once (perhaps to/from regular array ? or userspace ? -- depending on potential users) * (macro ?) iterate through elements (better have it ready for users of flex_array before, than convert their code later on) Oren. _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
