linux-kernel - RE: [PATCH] [RESEND] arm: limit memblock base address for early_pte

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Date:	Thu, 28 Jun 2012 14:43:17 +0900
From:	"Kim, Jong-Sung" <neidhard.kim@....com>
To:	"'Dave Martin'" <dave.martin@...aro.org>
Cc:	"'Minchan Kim'" <minchan@...nel.org>,
	"'Russell King'" <linux@....linux.org.uk>,
	"'Nicolas Pitre'" <nico@...aro.org>,
	"'Catalin Marinas'" <catalin.marinas@....com>,
	"'Chanho Min'" <chanho.min@....com>,
	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: RE: [PATCH] [RESEND] arm: limit memblock base address for early_pte_alloc

> From: Dave Martin [mailto:dave.martin@...aro.org]
> Sent: Thursday, June 28, 2012 1:02 AM
> 
> For me, it appears that this block just contains the initial region passed
> in ATAG_MEM or on the command line, with some reservations for
> swapper_pg_dir, the kernel text/data, device tree and initramfs.
> 
> So far as I can tell, the only memory guaranteed to be mapped here is the
> kernel image: there may be no guarantee that there is any unused space in
> this region which could be used to allocate extra page tables.
> The rest appears during the execution of map_lowmem().
> 
> Cheers
> ---Dave

Thank you for your comment, Dave! It was not that sophisticated choice, but
I thought that normal embedded system trying to reduce the BOM would have a
big-enough first memblock memory region. However you're right. There can be
exceptional systems. Then, how do you think about following manner:

diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
index e5dad60..0bc5316 100644
--- a/arch/arm/mm/mmu.c
+++ b/arch/arm/mm/mmu.c
@@ -1094,6 +1094,16 @@ static void __init kmap_init(void)
 static void __init map_lowmem(void)
 {
        struct memblock_region *reg;
+       phys_addr_t pmd_map_end = 0;
+
+       for_each_memblock(memory, reg) {
+               pmd_map_end = reg->base + reg->size;
+               if((reg->base | reg->size) & ~PMD_MASK)
+                       break;
+       }
+       if(pmd_map_end > lowmem_limit)
+               pmd_map_end = lowmem_limit;
+       memblock_set_current_limit(pmd_map_end & PMD_MASK);
 
        /* Map all the lowmem memory banks. */
        for_each_memblock(memory, reg) {
@@ -1113,6 +1123,8 @@ static void __init map_lowmem(void)
 
                create_mapping(&map);
        }
+
+       memblock_set_current_limit(lowmem_limit);
 }
 
 /*
@@ -1123,8 +1135,6 @@ void __init paging_init(struct machine_desc *mdesc)
 {
        void *zero_page;
 
-       memblock_set_current_limit(arm_lowmem_limit);
-
        build_mem_type_table();
        prepare_page_table();
        map_lowmem();

This will not limit the PTE-allocation to near the end of first bank.



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