Date: Thu, 15 Jul 2010 20:24:53 +0530 From: kalash nainwal <kalash.nainwal@gmail.com> To: John Baldwin <jhb@freebsd.org> Cc: freebsd-hackers@freebsd.org Subject: Re: how to do page level mem alloc in freebsd kernel? Message-ID: <AANLkTilkxsfj-LsJ9-Al-nMnvrzpcjaGOwRFihRiHv-W@mail.gmail.com> In-Reply-To: <201007150811.11721.jhb@freebsd.org> References: <AANLkTikg2K95ffSL_dAnYIri_NnqUGarViVETjrew8EB@mail.gmail.com> <201007150811.11721.jhb@freebsd.org>
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On Thu, Jul 15, 2010 at 5:41 PM, John Baldwin <jhb@freebsd.org> wrote: > On Thursday, July 15, 2010 6:28:53 am kalash nainwal wrote: >> Hi, >> >> I want to allocate one (or more) pages in kernel space. >> I'm not sure what is the api in freebsd (something which >> is similar to __get_free_pages() of linux). >> >> Would malloc(4096, ...) guarantee that the returned >> address is aligned on page boundary? > > Well, malloc(PAGE_SIZE) will align it on a page boundary. :) =A0malloc(40= 96) > will be aligned on a 4096-byte boundary if PAGE_SIZE is >=3D 4096. =A0My > understanding is that objects returned from malloc() are aligned to the > smallest power-of-2 value >=3D the requested size up to a page. =A0Alloca= tions > larger than a page are page aligned. =A0So a malloc of 24 bytes or 32 byt= es is > 32-byte aligned for example. > Thanks John for explaining. After going through the kernel src I was not sure about malloc, as the code is little hard to follow. However I figured kmem_alloc(kernel_pmap, PAGE_SIZE) would serve my purpose fine. Regards, -Kalash
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