b7761f1f08
When bus_dmamap_create is called, if bouncing might be required we reserve enough pages for a maximum-length request, subject to the MAX_BPAGES constraint (32 MB on amd64; 32 MB or 2 MB on i386 depending on the amount of RAM). Since pages used for bouncing are typically non-consecutive, each bounced page will typically constitute a busdma segment; as such, we are unlikely to ever successfully use more pages than the nsegments limit. Limit the number of pages reserved to nsegments. On FreeBSD/Firecracker, this reduces bounce page memory consumption from 32 MB to 512 kB, making VMs with 128 MB of RAM usable. Reviewed by: imp, mav Sponsored by: https://www.patreon.com/cperciva Differential Revision: https://reviews.freebsd.org/D37082 |
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