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module: Fix performance regression on modules with large symbol tables 

Looking at /proc/kallsyms, one starts to ponder whether all of the extra
strtab-related complexity in module.c is worth the memory savings.

Instead of making the add_kallsyms() loop even more complex, I tried the
other route of deleting the strmap logic and naively copying each string
into core_strtab with no consideration for consolidating duplicates.

Performance on an "already exists" insmod of nvidia.ko (runs
add_kallsyms() but does not actually initialize the module):

	Original scheme: 1.230s
	With naive copying: 0.058s

Extra space used: 35k (of a 408k module).

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
LKML-Reference: <73defb5e4bca04a6431392cc341112b1@localhost>
This commit is contained in:
Kevin Cernekee 2012-01-13 09:32:14 +10:30 committed by Rusty Russell
parent 70b1e9161e
commit 48fd11880b
1 changed files with 21 additions and 44 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

65
kernel/module.c
View File

@ -138,7 +138,6 @@ struct load_info {
unsigned long len;
Elf_Shdr *sechdrs;
char *secstrings, *strtab;
unsigned long *strmap;
unsigned long symoffs, stroffs;
struct _ddebug *debug;
unsigned int num_debug;
@ -2178,12 +2177,19 @@ static bool is_core_symbol(const Elf_Sym *src, const Elf_Shdr *sechdrs,
return true;
}
/*
* We only allocate and copy the strings needed by the parts of symtab
* we keep. This is simple, but has the effect of making multiple
* copies of duplicates. We could be more sophisticated, see
* linux-kernel thread starting with
* <73defb5e4bca04a6431392cc341112b1@localhost>.
*/
static void layout_symtab(struct module *mod, struct load_info *info)
{
Elf_Shdr *symsect = info->sechdrs + info->index.sym;
Elf_Shdr *strsect = info->sechdrs + info->index.str;
const Elf_Sym *src;
unsigned int i, nsrc, ndst;
unsigned int i, nsrc, ndst, strtab_size;
/* Put symbol section at end of init part of module. */
symsect->sh_flags |= SHF_ALLOC;
@ -2194,38 +2200,23 @@ static void layout_symtab(struct module *mod, struct load_info *info)
src = (void *)info->hdr + symsect->sh_offset;
nsrc = symsect->sh_size / sizeof(*src);
/*
* info->strmap has a '1' bit for each byte of .strtab we want to
* keep resident in mod->core_strtab. Everything else in .strtab
* is unreferenced by the symbols in mod->core_symtab, and will be
* discarded when add_kallsyms() compacts the string table.
*/
for (ndst = i = 1; i < nsrc; ++i, ++src)
/* Compute total space required for the core symbols' strtab. */
for (ndst = i = strtab_size = 1; i < nsrc; ++i, ++src)
if (is_core_symbol(src, info->sechdrs, info->hdr->e_shnum)) {
unsigned int j = src->st_name;
while (!__test_and_set_bit(j, info->strmap)
&& info->strtab[j])
++j;
++ndst;
strtab_size += strlen(&info->strtab[src->st_name]) + 1;
ndst++;
}
/* Append room for core symbols at end of core part. */
info->symoffs = ALIGN(mod->core_size, symsect->sh_addralign ?: 1);
mod->core_size = info->symoffs + ndst * sizeof(Elf_Sym);
info->stroffs = mod->core_size = info->symoffs + ndst * sizeof(Elf_Sym);
mod->core_size += strtab_size;
/* Put string table section at end of init part of module. */
strsect->sh_flags |= SHF_ALLOC;
strsect->sh_entsize = get_offset(mod, &mod->init_size, strsect,
info->index.str) | INIT_OFFSET_MASK;
DEBUGP("\t%s\n", info->secstrings + strsect->sh_name);
/* Append room for core symbols' strings at end of core part. */
info->stroffs = mod->core_size;
/* First strtab byte (and first symtab entry) are zeroes. */
__set_bit(0, info->strmap);
mod->core_size += bitmap_weight(info->strmap, strsect->sh_size);
}
static void add_kallsyms(struct module *mod, const struct load_info *info)
@ -2246,22 +2237,19 @@ static void add_kallsyms(struct module *mod, const struct load_info *info)
mod->symtab[i].st_info = elf_type(&mod->symtab[i], info);
mod->core_symtab = dst = mod->module_core + info->symoffs;
mod->core_strtab = s = mod->module_core + info->stroffs;
src = mod->symtab;
*dst = *src;
*s++ = 0;
for (ndst = i = 1; i < mod->num_symtab; ++i, ++src) {
if (!is_core_symbol(src, info->sechdrs, info->hdr->e_shnum))
continue;
dst[ndst] = *src;
dst[ndst].st_name = bitmap_weight(info->strmap,
dst[ndst].st_name);
++ndst;
dst[ndst++].st_name = s - mod->core_strtab;
s += strlcpy(s, &mod->strtab[src->st_name], KSYM_NAME_LEN) + 1;
}
mod->core_num_syms = ndst;
mod->core_strtab = s = mod->module_core + info->stroffs;
for (*s = 0, i = 1; i < info->sechdrs[info->index.str].sh_size; ++i)
if (test_bit(i, info->strmap))
*++s = mod->strtab[i];
}
#else
static inline void layout_symtab(struct module *mod, struct load_info *info)
@ -2751,27 +2739,18 @@ static struct module *layout_and_allocate(struct load_info *info)
this is done generically; there doesn't appear to be any
special cases for the architectures. */
layout_sections(mod, info);
info->strmap = kzalloc(BITS_TO_LONGS(info->sechdrs[info->index.str].sh_size)
* sizeof(long), GFP_KERNEL);
if (!info->strmap) {
err = -ENOMEM;
goto free_percpu;
}
layout_symtab(mod, info);
/* Allocate and move to the final place */
err = move_module(mod, info);
if (err)
goto free_strmap;
goto free_percpu;
/* Module has been copied to its final place now: return it. */
mod = (void *)info->sechdrs[info->index.mod].sh_addr;
kmemleak_load_module(mod, info);
return mod;
free_strmap:
kfree(info->strmap);
free_percpu:
percpu_modfree(mod);
out:
@ -2781,7 +2760,6 @@ out:
/* mod is no longer valid after this! */
static void module_deallocate(struct module *mod, struct load_info *info)
{
kfree(info->strmap);
percpu_modfree(mod);
module_free(mod, mod->module_init);
module_free(mod, mod->module_core);
@ -2911,8 +2889,7 @@ static struct module *load_module(void __user *umod,
if (err < 0)
goto unlink;
/* Get rid of temporary copy and strmap. */
kfree(info.strmap);
/* Get rid of temporary copy. */
free_copy(&info);
/* Done! */