[RFC PATCH v2 00/48] Make U-Boot memory reservations coherent

[Simon Glass]

Hi Sugosh,

On Mon, 8 Jul 2024 at 15:35, Tom Rini <trini at konsulko.com> wrote:
>
> On Thu, Jul 04, 2024 at 01:04:56PM +0530, Sughosh Ganu wrote:

I don't believe coherent is the right word here. Perhaps 'more
persistent' is better?

>
> > The aim of this patch series is to fix the current state of
> > incoherence between modules when it comes to memory usage. The primary
> > issue that this series is trying to fix is that the EFI memory module
> > which is responsible for allocating and freeing memory, does not have
> > any visibility of the memory that is being used by the LMB
> > module. This is further complicated by the fact that the LMB
> > allocations are caller specific -- the LMB memory map is not global
> > nor persistent. This means that the memory "allocated" by the LMB
> > module might be relevant only for a given function. Hence one of the
> > requirements for making the memory usage visible across modules is to
> > make LMB allocations persistent and global, and then have means to
> > communicate the use of memory across modules.
> >
> > The first set of patches in this series work on making the LMB memory
> > map persistent and global. This is being done keeping in mind the
> > usage of LMB memory by platforms where the same memory region can be
> > used to load multiple different images. What is not allowed is to
> > overwrite memory that has been allocated by the other module,
> > currently the EFI memory module. This is being achieved by introducing
> > a new flag, LMB_NOOVERWRITE, which represents memory which cannot be
> > re-requested once allocated.
> >
> > A review comment on the earlier version was to do away with the static
> > arrays for the LMB lists of free and used memory. This version
> > uses the alloced list data structure for the LMB lists.
> >
> > The second set of patches are making changes to the EFI memory module
> > to make use of the LMB functions to allocate and free memory. A
> > *_flags() version of LMB API's has been introduced for the same. The
> > earlier version was using notification mechanism from both LMB and EFI
> > modules to maintain memory coherence. This version makes use of the
> > LMB API functions for the memory allocations. This is based on review
> > comments of EFI maintainers.
>
> Please re-work so that the series is bisectable. For example
> xilinx_zynqmp_r5 fails that check currently. And I found that looking in
> to why it grows by ~1500 bytes overall. This likely is due to
> CONFIG_EFI_LOADER=n and so while the case where EFI_LOADER is enabled
> tends to be a size win (reduction) or wash we need to look at the
> CONFIG_EFI_LOADER=n case more. The alist code will be a little growth
> and that's fine enough. But realloc and do_bdinfo are the two big
> growths at the top, in this case.
>
> --
> Tom

Regards,
Simon