Messages in this thread | | | Subject | Re: [PATCH v2 0/6] Introduce ZONE_CMA | From | Vlastimil Babka <> | Date | Mon, 2 May 2016 09:49:47 +0200 |
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On 05/02/2016 08:14 AM, Joonsoo Kim wrote: >>> > >Although it's separate issue, I should mentioned one thing. Related to >>> > >I/O pinning issue, ZONE_CMA don't get blockdev allocation request so >>> > >I/O pinning problem is much reduced. >>> > > >> > >> >This is not super-clear from the patch. blockdev is using GFP_USER so it >> >already should not be classed as MOVABLE. I could easily be looking in >> >the wrong place or missed which allocation path sets GFP_MOVABLE. > Okay. Please see sb_bread(), sb_getblk(), __getblk() and __bread() in > include/linux/buffer_head.h. These are main functions used by blockdev > and they uses GFP_MOVABLE. To fix permanent allocation case which is > used by mount and cannot be released until umount, Gioh introduces > sb_bread_unmovable() but there are many remaining issues that prevent > migration at the moment and avoid blockdev allocation from CMA area is > preferable approach.
Hm Patch 3/6 describes the lack of blockdev allocations mostly as a limitation, although it does mention the possible advantages later. Anyway, this doesn't have to be specific to ZONE_CMA, right? You could just change ALLOC_CMA handling to consider GFP_HIGHUSER_MOVABLE instead of just __GFP_MOVABLE. For ZONE_CMA it might be inevitable as you describe, but it's already possible to do that now, if the advantages are larger than the disadvantages.
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