Re: [PATCH v2 1/2] mm/memblock: Add "reserve_mem" to reserved named memory at boot up

[Steven Rostedt <rostedt@goodmis.org>]

On Wed, 12 Jun 2024 07:23:40 +0000
Wei Yang <richard.weiyang@gmail.com> wrote:
> >> >+struct reserve_mem_table {
> >> >+	char			name[RESERVE_MEM_NAME_SIZE];
> >> >+	unsigned long		start;
> >> >+	unsigned long		size;    
> >> 
> >> phys_addr_t looks more precise?  
> >
> >For just the start variable, correct? I'm OK with updating that.
> >  
> 
> Both start and size. When you look at the definition of memblock_region, both
> are defined as phys_addr_t.

I ended up keeping everything phys_addr_t.

> 
> >>   
> >> >+};
> >> >+static struct reserve_mem_table reserved_mem_table[RESERVE_MEM_MAX_ENTRIES];
> >> >+static int reserved_mem_count;    
> >> 
> >> Seems no matter we use this feature or not, these memory would be occupied?  
> >
> >Yes, because allocation may screw it up as well. I could add a CONFIG
> >around it, so that those that do not want this could configure it out. But
> >since it's just a total of (16 + 8 + 8) * 8 = 256 bytes, I'm not sure it's
> >much of a worry to add the complexities to save that much space. As the
> >code to save it may likely be bigger.
> >  
> 
> If Mike feel good to it, I am ok.
> 
> >>   
> >> >+
> >> >+/* Add wildcard region with a lookup name */
> >> >+static int __init reserved_mem_add(unsigned long start, unsigned long size,
> >> >+				   const char *name)
> >> >+{
> >> >+	struct reserve_mem_table *map;
> >> >+
> >> >+	if (!name || !name[0] || strlen(name) >= RESERVE_MEM_NAME_SIZE)
> >> >+		return -EINVAL;
> >> >+
> >> >+	if (reserved_mem_count >= RESERVE_MEM_MAX_ENTRIES)
> >> >+		return -1;    
> >> 
> >> return ENOSPC? Not good at it, but a raw value maybe not a good practice.  
> >
> >This is what gets returned by the command line parser. It only cares if it
> >is zero or not.
> >  
> >> 
> >> Also, we'd better do this check before allocation.  
> >
> >What allocation?
> >  
> 
> You call reserved_mem_add() after memblock_phys_alloc(). 
> My suggestion is do those sanity check before calling memblock_phys_alloc().

Yeah, I did add more checks before the allocation happens.


> 
> >>   
> >> >+
> >> >+	map = &reserved_mem_table[reserved_mem_count++];
> >> >+	map->start = start;
> >> >+	map->size = size;
> >> >+	strscpy(map->name, name);
> >> >+	return 0;
> >> >+}
> >> >+
> >> >+/**
> >> >+ * reserve_mem_find_by_name - Find reserved memory region with a given name
> >> >+ * @name: The name that is attached to a reserved memory region
> >> >+ * @start: If found, holds the start address
> >> >+ * @size: If found, holds the size of the address.
> >> >+ *
> >> >+ * Returns: 1 if found or 0 if not found.
> >> >+ */
> >> >+int reserve_mem_find_by_name(const char *name, unsigned long *start, unsigned long *size)
> >> >+{
> >> >+	struct reserve_mem_table *map;
> >> >+	int i;
> >> >+
> >> >+	for (i = 0; i < reserved_mem_count; i++) {
> >> >+		map = &reserved_mem_table[i];
> >> >+		if (!map->size)
> >> >+			continue;
> >> >+		if (strcmp(name, map->name) == 0) {
> >> >+			*start = map->start;
> >> >+			*size = map->size;
> >> >+			return 1;
> >> >+		}
> >> >+	}
> >> >+	return 0;
> >> >+}
> >> >+
> >> >+/*
> >> >+ * Parse early_reserve_mem=nn:align:name    
> >> 
> >> early_reserve_mem or reserve_mem ?  
> >
> >Oops, that was the original name. I'll change that.
> >  
> >>   
> >> >+ */
> >> >+static int __init reserve_mem(char *p)
> >> >+{
> >> >+	phys_addr_t start, size, align;  
> >
> >Hmm, I wonder if I should change size and align to unsigned long?
> >  
> 
> I grep the kernel, some use u64, some use unsigned long. 
> I think it is ok to use unsigned long here.

For consistency, I switched them all to phys_addr_t.

> 
> >> >+	char *oldp;
> >> >+	int err;
> >> >+
> >> >+	if (!p)
> >> >+		return -EINVAL;
> >> >+
> >> >+	oldp = p;
> >> >+	size = memparse(p, &p);
> >> >+	if (p == oldp)
> >> >+		return -EINVAL;
> >> >+
> >> >+	if (*p != ':')
> >> >+		return -EINVAL;
> >> >+
> >> >+	align = memparse(p+1, &p);
> >> >+	if (*p != ':')
> >> >+		return -EINVAL;
> >> >+    
> >> 
> >> Better to check if the name is valid here.   
> >
> >You mean that it has text and is not blank?
> >  
> >> 
> >> Make sure command line parameters are valid before doing the allocation.  
> >
> >You mean that size is non zero?
> >  
> 
> I mean do those sanity check before real allocation.

Yep, I hope I caught everything (of course I need to check if the name
exists first).

> 
> >I don't know if we care what the align is. Zero is valid.
> >  
> 
> memblock internal would check the alignment. If it is zero, it will change to
> SMP_CACHE_BYTES with dump_stack().

I saw that and added:

	if (align < SMP_CACHE_BYTES)
		align = SMP_CACHE_BYTES;

so that SMP_CACHE_BYTES will be the minimum alignment.

Thanks for looking at this.

-- Steve