On 02/15/2013 09:26 PM, Ric Mason wrote: > On 02/14/2013 02:38 AM, Seth Jennings wrote: >> ========= >> DO NOT MERGE, FOR REVIEW ONLY >> This patch introduces zsmalloc as new code, however, it already >> exists in drivers/staging. In order to build successfully, you >> must select EITHER to driver/staging version OR this version. >> Once zsmalloc is reviewed in this format (and hopefully accepted), >> I will create a new patchset that properly promotes zsmalloc from >> staging. >> ========= >> >> This patchset introduces a new slab-based memory allocator, >> zsmalloc, for storing compressed pages. It is designed for >> low fragmentation and high allocation success rate on >> large object, but <= PAGE_SIZE allocations. >> >> zsmalloc differs from the kernel slab allocator in two primary >> ways to achieve these design goals. >> >> zsmalloc never requires high order page allocations to back >> slabs, or "size classes" in zsmalloc terms. Instead it allows >> multiple single-order pages to be stitched together into a >> "zspage" which backs the slab. This allows for higher allocation >> success rate under memory pressure. >> >> Also, zsmalloc allows objects to span page boundaries within the >> zspage. This allows for lower fragmentation than could be had >> with the kernel slab allocator for objects between PAGE_SIZE/2 >> and PAGE_SIZE. With the kernel slab allocator, if a page compresses >> to 60% of it original size, the memory savings gained through >> compression is lost in fragmentation because another object of >> the same size can't be stored in the leftover space. > > Why you say so? slab/slub allocator both have policies to setup > suitable order of pages in each slab cache in order to reduce > fragmentation. Which codes show you slab object can't span page > boundaries? Could you pointed out to me? I might need to reword this. What I meant to say is "non-contiguous page boundaries". zsmalloc allows an object to span non-contiguous page boundaries within a zspage. This obviously can't be done by slab/slub since they give addresses directly to users and the object data must be contiguous. This is one reason why zsmalloc allocations require mapping to obtain a usable address. Thanks, Seth _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/devel
