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Message #169691
[Bug 1563293] [NEW] linux: exclude ZONE_DEVICE from GFP_ZONE_TABLE
Public bug reported:
mm: exclude ZONE_DEVICE from GFP_ZONE_TABLE
ZONE_DEVICE (merged in 4.3) and ZONE_CMA (proposed) are examples of new
mm zones that are bumping up against the current maximum limit of 4
zones, i.e. 2 bits in page->flags for the GFP_ZONE_TABLE.
The GFP_ZONE_TABLE poses an interesting constraint since
include/linux/gfp.h gets included by the 32-bit portion of a 64-bit
build. We need to be careful to only build the table for zones that
have a corresponding gfp_t flag. GFP_ZONES_SHIFT is introduced for this
purpose. This patch does not attempt to solve the problem of adding a
new zone that also has a corresponding GFP_ flag.
Vlastimil points out that ZONE_DEVICE, by depending on x86_64 and
SPARSEMEM_VMEMMAP implies that SECTIONS_WIDTH is zero. In other words
even though ZONE_DEVICE does not fit in GFP_ZONE_TABLE it is free to
consume another bit in page->flags (expand ZONES_WIDTH) with room to
spare.
** Affects: linux (Ubuntu)
Importance: Undecided
Assignee: Tim Gardner (timg-tpi)
Status: Fix Committed
** Affects: linux (Ubuntu Xenial)
Importance: Undecided
Assignee: Tim Gardner (timg-tpi)
Status: Fix Committed
** Also affects: linux (Ubuntu Xenial)
Importance: Undecided
Status: New
** Changed in: linux (Ubuntu Xenial)
Status: New => Fix Committed
** Changed in: linux (Ubuntu Xenial)
Assignee: (unassigned) => Tim Gardner (timg-tpi)
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https://bugs.launchpad.net/bugs/1563293
Title:
linux: exclude ZONE_DEVICE from GFP_ZONE_TABLE
Status in linux package in Ubuntu:
Fix Committed
Status in linux source package in Xenial:
Fix Committed
Bug description:
mm: exclude ZONE_DEVICE from GFP_ZONE_TABLE
ZONE_DEVICE (merged in 4.3) and ZONE_CMA (proposed) are examples of new
mm zones that are bumping up against the current maximum limit of 4
zones, i.e. 2 bits in page->flags for the GFP_ZONE_TABLE.
The GFP_ZONE_TABLE poses an interesting constraint since
include/linux/gfp.h gets included by the 32-bit portion of a 64-bit
build. We need to be careful to only build the table for zones that
have a corresponding gfp_t flag. GFP_ZONES_SHIFT is introduced for this
purpose. This patch does not attempt to solve the problem of adding a
new zone that also has a corresponding GFP_ flag.
Vlastimil points out that ZONE_DEVICE, by depending on x86_64 and
SPARSEMEM_VMEMMAP implies that SECTIONS_WIDTH is zero. In other words
even though ZONE_DEVICE does not fit in GFP_ZONE_TABLE it is free to
consume another bit in page->flags (expand ZONES_WIDTH) with room to
spare.
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