Re: [PATCH v4] mm/vmstat: add events for ksm cow

kernel test robot
2022-03-30T13:30:17Z

Hi,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on hnaz-mm/master]

url: https://github.com/intel-lab-lkp/linux/commits/cgel-zte-gmail-com/mm-vmstat-add-events-for-ksm-cow/20220330-162859
base: https://github.com/hnaz/linux-mm master
config: nios2-buildonly-randconfig-r001-20220330 (https://download.01.org/0day-ci/archive/20220330/202203302122.cFR0tu2M-lkp@intel.com/config)
compiler: nios2-linux-gcc (GCC) 11.2.0
reproduce (this is a W=1 build):
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# https://github.com/intel-lab-lkp/linux/commit/48bd13bff24d30af750dd9429638a2563b758611
git remote add linux-review https://github.com/intel-lab-lkp/linux
git fetch --no-tags linux-review cgel-zte-gmail-com/mm-vmstat-add-events-for-ksm-cow/20220330-162859
git checkout 48bd13bff24d30af750dd9429638a2563b758611
# save the config file to linux build tree
mkdir build_dir
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.2.0 make.cross O=build_dir ARCH=nios2 SHELL=/bin/bash

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

mm/memory.c: In function 'do_wp_page':
>> mm/memory.c:3336:32: error: 'COW_KSM' undeclared (first use in this function)
3336 | count_vm_event(COW_KSM);
| ^~~~~~~
mm/memory.c:3336:32: note: each undeclared identifier is reported only once for each function it appears in

vim +/COW_KSM +3336 mm/memory.c

3229
3230 /*
3231 * This routine handles present pages, when users try to write
3232 * to a shared page. It is done by copying the page to a new address
3233 * and decrementing the shared-page counter for the old page.
3234 *
3235 * Note that this routine assumes that the protection checks have been
3236 * done by the caller (the low-level page fault routine in most cases).
3237 * Thus we can safely just mark it writable once we've done any necessary
3238 * COW.
3239 *
3240 * We also mark the page dirty at this point even though the page will
3241 * change only once the write actually happens. This avoids a few races,
3242 * and potentially makes it more efficient.
3243 *
3244 * We enter with non-exclusive mmap_lock (to exclude vma changes,
3245 * but allow concurrent faults), with pte both mapped and locked.
3246 * We return with mmap_lock still held, but pte unmapped and unlocked.
3247 */
3248 static vm_fault_t do_wp_page(struct vm_fault *vmf)
3249 __releases(vmf->ptl)
3250 {
3251 struct vm_area_struct *vma = vmf->vma;
3252
3253 if (userfaultfd_pte_wp(vma, *vmf->pte)) {
3254 pte_unmap_unlock(vmf->pte, vmf->ptl);
3255 return handle_userfault(vmf, VM_UFFD_WP);
3256 }
3257
3258 /*
3259 * Userfaultfd write-protect can defer flushes. Ensure the TLB
3260 * is flushed in this case before copying.
3261 */
3262 if (unlikely(userfaultfd_wp(vmf->vma) &&
3263 mm_tlb_flush_pending(vmf->vma->vm_mm)))
3264 flush_tlb_page(vmf->vma, vmf->address);
3265
3266 vmf->page = vm_normal_page(vma, vmf->address, vmf->orig_pte);
3267 if (!vmf->page) {
3268 /*
3269 * VM_MIXEDMAP !pfn_valid() case, or VM_SOFTDIRTY clear on a
3270 * VM_PFNMAP VMA.
3271 *
3272 * We should not cow pages in a shared writeable mapping.
3273 * Just mark the pages writable and/or call ops->pfn_mkwrite.
3274 */
3275 if ((vma->vm_flags & (VM_WRITE|VM_SHARED)) ==
3276 (VM_WRITE|VM_SHARED))
3277 return wp_pfn_shared(vmf);
3278
3279 pte_unmap_unlock(vmf->pte, vmf->ptl);
3280 return wp_page_copy(vmf);
3281 }
3282
3283 /*
3284 * Take out anonymous pages first, anonymous shared vmas are
3285 * not dirty accountable.
3286 */
3287 if (PageAnon(vmf->page)) {
3288 struct page *page = vmf->page;
3289
3290 /*
3291 * We have to verify under page lock: these early checks are
3292 * just an optimization to avoid locking the page and freeing
3293 * the swapcache if there is little hope that we can reuse.
3294 *
3295 * PageKsm() doesn't necessarily raise the page refcount.
3296 */
3297 if (PageKsm(page) || page_count(page) > 3)
3298 goto copy;
3299 if (!PageLRU(page))
3300 /*
3301 * Note: We cannot easily detect+handle references from
3302 * remote LRU pagevecs or references to PageLRU() pages.
3303 */
3304 lru_add_drain();
3305 if (page_count(page) > 1 + PageSwapCache(page))
3306 goto copy;
3307 if (!trylock_page(page))
3308 goto copy;
3309 if (PageSwapCache(page))
3310 try_to_free_swap(page);
3311 if (PageKsm(page) || page_count(page) != 1) {
3312 unlock_page(page);
3313 goto copy;
3314 }
3315 /*
3316 * Ok, we've got the only page reference from our mapping
3317 * and the page is locked, it's dark out, and we're wearing
3318 * sunglasses. Hit it.
3319 */
3320 unlock_page(page);
3321 wp_page_reuse(vmf);
3322 return VM_FAULT_WRITE;
3323 } else if (unlikely((vma->vm_flags & (VM_WRITE|VM_SHARED)) ==
3324 (VM_WRITE|VM_SHARED))) {
3325 return wp_page_shared(vmf);
3326 }
3327 copy:
3328 /*
3329 * Ok, we need to copy. Oh, well..
3330 */
3331 get_page(vmf->page);
3332
3333 pte_unmap_unlock(vmf->pte, vmf->ptl);
3334 #ifdef CONFIG_KSM
3335 if (PageKsm(vmf->page))
> 3336 count_vm_event(COW_KSM);
3337 #endif
3338 return wp_page_copy(vmf);
3339 }
3340

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