[SeaBIOS] Re: [PATCH v2 2/2] malloc: use large ZoneHigh when there is enough memory

[Kevin O'Connor]

On Mon, Apr 25, 2022 at 09:41:45AM +0200, Gerd Hoffmann wrote:
> In case there is enough memory installed use a large ZoneHigh.
> Signed-off-by: Gerd Hoffmann
>
> src/config.h | 3 ++-
>  src/malloc.c | 4 +++-
>  2 files changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/src/config.h b/src/config.h
> index 93c8dbc2d530..9abe355b6c47 100644
> --- a/src/config.h
> +++ b/src/config.h
> @@ -17,7 +17,8 @@
>  // Maximum number of map entries in the e820 map
>  #define BUILD_MAX_E820 32
>  // Space to reserve in high-memory for tables
> -#define BUILD_MAX_HIGHTABLE (256*1024)
> +#define BUILD_MIN_HIGHTABLE (256*1024)
> +#define BUILD_MAX_HIGHTABLE (16*1024*1024)
>  // Largest supported externaly facing drive id
>  #define BUILD_MAX_EXTDRIVE 16
>  // Number of bytes the smbios may be and still live in the f-segment
> diff --git a/src/malloc.c b/src/malloc.c
> index 7fa50a85595b..553164d53a38 100644
> --- a/src/malloc.c
> +++ b/src/malloc.c
> @@ -423,7 +423,7 @@ malloc_preinit(void)
>  // Populate temp high ram
>  u32 highram_start = 0;
> u32 highram_size = BUILD_MAX_HIGHTABLE;
> u32 highram_size = BUILD_MIN_HIGHTABLE;
> int i;
> for (i=e820_count-1; i>=0; i--) {
>     struct e820entry *en = &e820_list[i];
>
> @@ -434,6 +434,8 @@ malloc_preinit(void)
>              continue;
>          u32 s = en->start, e = end;
>          if (!highram_start) {
>        if (e > BUILD_MAX_HIGHTABLE * 16)
>            highram_size = BUILD_MAX_HIGHTABLE;
>        u32 newe = ALIGN_DOWN(e - highram_size, MALLOC_MIN_ALIGN);
>        if (newe <= e && newe >= s) {
>            highram_start = newe;

Thanks.  At a high-level, it looks fine.  However, I think the above
might introduce a corner case where a fragmented e820 might fail to
find any ZoneHigh.

Maybe something like the following instead:

u32 newe = ALIGN_DOWN(e - BUILD_MIN_HIGHTABLE, MALLOC_MIN_ALIGN);
             if (newe <= e && newe >= s) {
                 if (newe - s >= 20*1024*1024) {
                     highram_size = 16*1024*1024;
                     newe -= highram_size - BUILD_MIN_HIGHTABLE;
                 }
                 highram_start = e = newe;
             }

-Kevin