From mboxrd@z Thu Jan 1 00:00:00 1970 From: William Lee Irwin III Date: Thu, 15 Jul 2004 23:16:38 +0000 Subject: Re: free bootmem feedback patch Message-Id: <20040715231638.GY3411@holomorphy.com> List-Id: References: <40F46962.4090604@sgi.com> In-Reply-To: <40F46962.4090604@sgi.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ia64@vger.kernel.org On Thu, Jul 15, 2004 at 12:11:07PM -0700, Luck, Tony wrote: > Attached is my version that just frees pages in O(log2(BITS_PER_LONG)) > pieces ... because I'm too lazy to figure out all the boundary > conditions to implement wli's excellent suggestion. > On my 2G machine, this reduced the time to free all the bootmem > from 41ms to 18.1ms ... so it should shave some minutes off the > monster SGI box that started this thread, but perhaps not enough > to avoid the "looks like the system is hung" problem as you will > still be looking at a couple of minutes :-( Since I only got a > 55% reduction, rather than a factor of 64 I expect that modifying > to look an larger order pages may have diminishing returns. I'll work relative to this for the rest. I'd recommend using __ffs() instead of the loop. Also, combining this with a specialized page freeing function that doesn't e.g. fiddle with page references On Thu, Jul 15, 2004 at 12:11:07PM -0700, Luck, Tony wrote: > Notes and Caveats: > 1) Is there a define someplace for log2(BITS_PER_LONG)? I couldn't > find one, which is why I calculate the "order" in this patch. Unfortunately no. It would be nice to have one. On Thu, Jul 15, 2004 at 12:11:07PM -0700, Luck, Tony wrote: > 2) On ia64 it looks like the pages and the bitmap are nicely aligned > so that a longword in node_bootmem_map[] corresponds to an order 6 > page with the right physical alignment. This may not be true on other > architectures, and mm/bootmem.c is generic code. Before this patch > can go into the base, someone would have to check all the other > architectures (some of which might not care to change ... if they > only support 4G or less, then the benefits of saving a few milliseconds > during boot may not inspire them to mess with the boot code). For > this reason I'm not adding a "Signed-off-by" to this patch because > I don't want the flack for breaking other architectures ... but by > all means take this patch and try it out. The common case is the bitmap and mem_map[] starting at 0. The remaining cases are pretty marginalized. This can actually be checked at runtime by checking the alignment of ->node_boot_start, e.g. maybe if (!~v && !((__pa(bdata->node_boot_start) >> PAGE_SHIFT) & ((1 << MAX_ORDER) - 1))) instead of just !~v. -- wli