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Date: Wed, 12 Jun 2024 07:23:40 +0000
From: Wei Yang <richard.weiyang@gmail.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Wei Yang <richard.weiyang@gmail.com>, linux-kernel@vger.kernel.org,
	linux-trace-kernel@vger.kernel.org,
	Masami Hiramatsu <mhiramat@kernel.org>,
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	Mike Rapoport <rppt@kernel.org>
Subject: Re: [PATCH v2 1/2] mm/memblock: Add "reserve_mem" to reserved named
 memory at boot up
Message-ID: <20240612072340.hsdxusmszixebvrt@master>
Reply-To: Wei Yang <richard.weiyang@gmail.com>
References: <20240606150143.876469296@goodmis.org>
 <20240606150316.751642266@goodmis.org>
 <20240611144029.h7egl4aif5mjlrwf@master>
 <20240611111218.71e57e0f@gandalf.local.home>
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On Tue, Jun 11, 2024 at 11:12:18AM -0400, Steven Rostedt wrote:
>On Tue, 11 Jun 2024 14:40:29 +0000
>Wei Yang <richard.weiyang@gmail.com> wrote:
>
>Missed this just before sending out v3 :-p
>
>> >diff --git a/mm/memblock.c b/mm/memblock.c
>> >index d09136e040d3..a8bf0ee9e2b4 100644
>> >--- a/mm/memblock.c
>> >+++ b/mm/memblock.c
>> >@@ -2244,6 +2244,103 @@ void __init memblock_free_all(void)
>> > 	totalram_pages_add(pages);
>> > }
>> > 
>> >+/* Keep a table to reserve named memory */
>> >+#define RESERVE_MEM_MAX_ENTRIES		8
>> >+#define RESERVE_MEM_NAME_SIZE		16  
>>                                         ^
>> Suggest to align with previous line.
>
>It is. But because the patch adds a "+", it pushed the "8" out another tab.
>
>> 
>> >+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.

>> 
>> >+};
>> >+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().

>> 
>> >+
>> >+	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.

>> >+	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.

>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().

>> 
>> >+	start = memblock_phys_alloc(size, align);
>> >+	if (!start)
>> >+		return -ENOMEM;
>> >+
>> >+	p++;
>> >+	err = reserved_mem_add(start, size, p);
>> >+	if (err) {
>> >+		memblock_phys_free(start, size);
>> >+		return err;
>> >+	}
>> >+
>> >+	p += strlen(p);
>> >+
>> >+	return *p == '\0' ? 0: -EINVAL;  
>> 
>> We won't free the memory if return -EINVAL?
>
>I guess we can do this check before the allocation, like you suggested.
>
>Thanks for the review.
>
>-- Steve
>
>
>> 
>> >+}
>> >+__setup("reserve_mem=", reserve_mem);
>> >+
>> > #if defined(CONFIG_DEBUG_FS) && defined(CONFIG_ARCH_KEEP_MEMBLOCK)
>> > static const char * const flagname[] = {
>> > 	[ilog2(MEMBLOCK_HOTPLUG)] = "HOTPLUG",
>> >-- 
>> >2.43.0
>> >
>> >  
>> 

-- 
Wei Yang
Help you, Help me