On Fri, Jan 31, 2020 at 9:43 AM Robin Murphy <robin.mur...@arm.com> wrote: > > On 31/01/2020 2:42 pm, Eric Dumazet wrote: > > On Fri, Jan 31, 2020 at 4:30 AM Robin Murphy <robin.mur...@arm.com> wrote: > >> > >> ...and when that represents ~5% of the total system RAM it is a *lot* > >> less reasonable than even 12KB. As I said, it's great to make a debug > >> option more efficient such that what it observes is more representative > >> of the non-debug behaviour, but it mustn't come at the cost of making > >> the entire option unworkable for other users. > >> > > > > Then I suggest you send a patch to reduce PREALLOC_DMA_DEBUG_ENTRIES > > because having 65536 preallocated entries consume 4 MB of memory. > > ...unless it's overridden on the command-line ;) > > > Actually this whole attempt to re-implement slab allocations in this > > file is suspect. > > Again that's a matter of expected usage patterns - typically the > "reasonable default" or user-defined preallocation should still be > enough (as it *had* to be before), and the kind of systems that can > sustain so many live mappings as to regularly hit the dynamic expansion > path are also likely to have enough memory not to care that later-unused > entries never get 'properly' freed back to the kernel (plus as you've > observed, many workloads tend to reach a steady state where entries are > mostly only transiently free anyway). The reasoning for the exact > implementation details is there in the commit logs. > > > Do not get me wrong, but if you really want to run linux on a 16MB host, > > I guess you need to add CONFIG_BASE_SMALL all over the places, > > not only in this kernel/dma/debug.c file. > > Right, nobody's suggesting that defconfig should "just work" on your > router/watch/IoT shoelaces/whatever, I'm just saying that tuning any > piece of common code for datacenter behemoths, for quality-of-life > rather than functional necessity, and leaving no way to adjust it other > than hacking the source, would represent an unnecessary degree of > short-sightedness that we can and should avoid. > > Taking a closer look at the code, it appears fairly straightforward to > make the hash size variable, and in fact making it self-adjusting > doesn't seem too big a jump from there. I'm happy to have a go at that > myself if you like.
Sure, go ahead, I have no plan implementing changes for 20 years old platforms. Thanks. _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu