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 A7cO3PIx czuqgwYiDYnRA3bRjpNGg5WUoi+Kju9tmoGbvmPbZPoynKaxEoauWe7GYHaDuJMHM9Yr9bxumuo1NDBeZszyZWi2+7bXTb37294puEiCAcFaNKOSRmSsxbhfVL19px8mQ8rijipRA+BtrTKqlhBDkw38c6izVQZeUEQ5ROnGNxl0LBmlUSsjoI4Hw5Gtfw1xzVP04e2LVQlz9n1sXrZRbK6AlqGME8Ut7PR25bdgr95TQEHRC5rIbpH9VrVk9BjRlUv8aFf+UX35DSw7N5dNxSxjIhehkKgF9+xhVMhihCJqeriy9nV0J0YwftUtzihOR7HogYFAyCRuYTISQetm43wsrHOMLett3/zY9P9PukIKDcNbXmHh83xs5SBfm8x/fnr0nPl1LdzFyXejdufgzl+T53ltJZCYukYkECBiAll4fCIFTcg4GFB+YlNhd8S6mzWmE5wYNFynBMFi+NJnXU3y+i9uFKiI6wTMP X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 1/11/2026 4:59 PM, David Hildenbrand (Red Hat) wrote: > On 1/10/26 19:20, Garg, Shivank wrote: >> >> >> On 1/9/2026 8:16 PM, David Hildenbrand (Red Hat) wrote: >>> On 12/15/25 09:46, Shivank Garg wrote: >>> >>> This looks a bit complicated. Can't we move that handing up, where we have most of that >>> information already? Or am I missing something important? >>> >>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >>> index 97d1b2824386f..c7271877c5220 100644 >>> --- a/mm/khugepaged.c >>> +++ b/mm/khugepaged.c >>> @@ -22,6 +22,7 @@ >>>   #include >>>   #include >>>   #include >>> +#include >>>     #include >>>   #include "internal.h" >>> @@ -2786,7 +2787,9 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, >>>            for (addr = hstart; addr < hend; addr += HPAGE_PMD_SIZE) { >>>                  int result = SCAN_FAIL; >>> +               bool triggered_wb = false; >>>   +retry: >>>                  if (!mmap_locked) { >>>                          cond_resched(); >>>                          mmap_read_lock(mm); >>> @@ -2809,6 +2812,16 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, >>>                          mmap_locked = false; >>             >>               *lock_dropped = true; >>>                          result = hpage_collapse_scan_file(mm, addr, file, pgoff, >>>                                                            cc); >>> + >>> +                       if (result == SCAN_PAGE_DIRTY_OR_WRITEBACK && !triggered_wb && >>> +                           mapping_can_writeback(file->f_mapping)) { >>> +                               loff_t lstart = (loff_t)pgoff << PAGE_SHIFT; >>> +                               loff_t lend = lstart + HPAGE_PMD_SIZE - 1; >>> + >>> +                               filemap_write_and_wait_range(file->f_mapping, lstart, lend); >>> +                               triggered_wb = true; >> >>                   fput(file); >> >>> +                               goto retry; >>> +                       } >>>                          fput(file); >>>                  } else { >>>                          result = hpage_collapse_scan_pmd(mm, vma, addr, >>> >>> >> >> Thank you for the suggestion, this approach looks much simpler. >> >> There are two small nits I observed: > > Yeah, was a quick untested hack to see if this can be simplified :) > >> >> 1. In the retry loop, it is possible that we reacquire the mmap_lock and set >>     mmap_locked to true. This can cause issues later when we do: >> >>         if (!mmap_locked) >>                 *lock_dropped = true; > > That whole logic of having two variables that express whether locks have been taken/dropped is just absolutely confusing. Any way we can clean that up? > >> >>     because the caller would no longer see that the lock was dropped earlier. >> >> 2. We need an fput() to balance the file reference taken at line 2795. > > Ah, yes, makes sense. Having a single fput() would be nicer, but that would require yet another temporary variable. > I agree, that this interaction for lock taken/droped is confusing. However, a proper clean-up would require refactoring the locking logic across multiple functions in the collapse call-flow path. This seems significantly more invasive and risky. I would like to handle this refactoring but in a separate TODO for later. Could we please proceed with these minimal changes for now? Since, V4 has been in the linux-next/mm-unstable for a while, should I send a v5 or an incremental clean-up on top for this? Thanks, Shivank