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Date: Fri, 16 Jan 2009 20:42:27 +0900
From: KOSAKI Motohiro <kosaki.motohiro@...il.com>
To: Trilok Soni <soni.trilok@...il.com>
Cc: Greg KH <greg@...ah.com>,
Arve Hjønnevåg <arve@...roid.com>,
Alan Cox <alan@...rguk.ukuu.org.uk>,
Pavel Machek <pavel@...e.cz>,
Brian Swetland <swetland@...gle.com>, arve@...gle.com,
San Mehat <san@...roid.com>, Robert Love <rlove@...gle.com>,
linux-kernel@...r.kernel.org,
"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
Tony Lindgren <tony@...mide.com>,
ext Juha Yrjölä <juha.yrjola@...idboot.com>,
viktor.rosendahl@...ia.com
Subject: Re: lowmemory android driver not needed?
> And there is one more lowmem driver developed by Nokia for Nokia 8xx
> tablets it seems. CCed Tony Lindgren, Juha and Viktor.
>
> http://git.kernel.org/?p=linux/kernel/git/tmlind/linux-omap-2.6.git;a=blob;f=security/lowmem.c;h=ae78a530af39703e335ad769f1e6f097f63ec6dd;hb=HEAD
quick review.
> 325 static struct security_operations lowmem_security_ops = {
> 326 /* Use the capability functions for some of the hooks */
> 327 .ptrace_may_access = cap_ptrace_may_access,
> 328 .ptrace_traceme = cap_ptrace_traceme,
> 329 .capget = cap_capget,
> 330 .capset_check = cap_capset_check,
> 331 .capset_set = cap_capset_set,
> 332 .capable = cap_capable,
> 333
> 334 .bprm_apply_creds = cap_bprm_apply_creds,
> 335 .bprm_set_security = cap_bprm_set_security,
> 336
> 337 .task_post_setuid = cap_task_post_setuid,
> 338 .task_reparent_to_init = cap_task_reparent_to_init,
> 339 .vm_enough_memory = low_vm_enough_memory,
> 340 };
.vm_enough_memory is the hook of virtual memory accounting, not rss.
modern almost linux application and glibc largely use virtual address space
than actual resident memory.
then, vm_enough_memory don't provide proper hook.
> 57 static ctl_table lowmem_table[] = {
> 58 {
> 59 .ctl_name = VM_LOWMEM_DENY_PAGES,
> 60 .procname = "lowmem_deny_watermark_pages",
> 61 .data = &deny_pages,
> 62 .maxlen = sizeof(long),
> 63 .mode = 0644,
> 64 .child = NULL,
> 65 .proc_handler = &proc_dointvec,
> 66 .strategy = &sysctl_intvec,
> 67 }, {
you can set .ctl_name to CTL_UNNUMBERED.
> 249 static int low_vm_enough_memory(struct mm_struct *mm, long pages)
> 250 {
> 251 unsigned long free, allowed;
> 252 int cap_sys_admin = 0, notify;
> 253
> 254 if (cap_capable(current, CAP_SYS_ADMIN) == 0)
> 255 cap_sys_admin = 1;
> 256
> 257 allowed = totalram_pages - hugetlb_total_pages();
> 258 allowed_pages = allowed;
> 259
> 260 /* We activate ourselves only after both parameters have been
> 261 * configured. */
> 262 if (deny_pages == 0 || notify_low_pages == 0 || notify_high_pages == 0)
> 263 return __vm_enough_memory(mm, pages, cap_sys_admin);
> 264
> 265 vm_acct_memory(pages);
> 266
> 267 /* Easily freed pages when under VM pressure or direct reclaim */
> 268 free = global_page_state(NR_FILE_PAGES);
this line assume file page can evictable. but it is not true.
we should consider mlocked file page.
> 269 free += nr_swap_pages;
> 270 free += global_page_state(NR_SLAB_RECLAIMABLE);
> 271
> 272 if (likely(free > notify_low_pages))
> 273 goto enough_memory;
> 274
> 275 /* No luck, lets make it more expensive and try again.. */
> 276 free += nr_free_pages();
> 277
> 278 if (free < deny_pages) {
> 279 int i;
> 280
> 281 lowmem_free_pages = free;
> 282 low_watermark_state(1);
> 283 high_watermark_state(1);
> 284 /* Memory allocations by root are always allowed */
> 285 if (cap_sys_admin)
> 286 return 0;
> 287
> 288 /* OOM unkillable process is allowed to consume memory */
> 289 if (current->oomkilladj == OOM_DISABLE)
> 290 return 0;
No generic assumption.
> 292 /* uids from allowed_uids vector are also allowed no matter what */
> 293 for (i = 0; i < LOWMEM_MAX_UIDS && allowed_uids[i]; i++)
> 294 if (current->uid == allowed_uids[i])
> 295 return 0;
Oops, LOWMEM_MAX_UIDS is ugly restriction.
> 297 vm_unacct_memory(pages);
> 298 if (printk_ratelimit()) {
> 299 printk(MY_NAME ": denying memory allocation to process %d (%s> )\n",
> 300 current->pid, current->comm);
> 301 }
> 302 return -ENOMEM;
> 303 }
> 304
> 305 enough_memory:
> 306 /* See if we need to notify level 1 */
> 307 low_watermark_state(free < notify_low_pages);
> 308
> 309 /*
> 310 * In the level 2 notification case things are more complicated,
> 311 * as the level that we drop the state and send a notification
> 312 * should be lower than when it is first triggered. Having this
> 313 * on the same watermark level ends up bouncing back and forth
> 314 * when applications are being stupid.
> 315 */
> 316 notify = free < notify_high_pages;
> 317 if (notify || free - nr_decay_pages > notify_high_pages)
> 318 high_watermark_state(notify);
> 319
> 320 /* We have plenty of memory */
> 321 lowmem_free_pages = free;
It seems racy.
if this code run on smp, lowmem_free_pages can hold unproper value.
> 322 return 0;
> 323 }
then, In my first look, this code deeply depend on embedded and nokia
process management policy.
I don't think it can merge mainline.
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