s390/gmap: improve THP splitting
During s390_enable_sie(), we need to take care of splitting all qemu user process THP mappings. This is currently done with follow_page(FOLL_SPLIT), by simply iterating over all vma ranges, with PAGE_SIZE increment. This logic is sub-optimal and can result in a lot of unnecessary overhead, especially when using qemu and ASAN with large shadow map. Ilya reported significant system slow-down with one CPU busy for a long time and overall unresponsiveness. Fix this by using walk_page_vma() and directly calling split_huge_pmd() only for present pmds, which greatly reduces overhead. Cc: <stable@vger.kernel.org> # v5.4+ Reported-by: Ilya Leoshkevich <iii@linux.ibm.com> Tested-by: Ilya Leoshkevich <iii@linux.ibm.com> Acked-by: Christian Borntraeger <borntraeger@de.ibm.com> Signed-off-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com> Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
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@ -2485,23 +2485,36 @@ void gmap_sync_dirty_log_pmd(struct gmap *gmap, unsigned long bitmap[4],
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}
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EXPORT_SYMBOL_GPL(gmap_sync_dirty_log_pmd);
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#ifdef CONFIG_TRANSPARENT_HUGEPAGE
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static int thp_split_walk_pmd_entry(pmd_t *pmd, unsigned long addr,
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unsigned long end, struct mm_walk *walk)
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{
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struct vm_area_struct *vma = walk->vma;
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split_huge_pmd(vma, pmd, addr);
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return 0;
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}
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static const struct mm_walk_ops thp_split_walk_ops = {
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.pmd_entry = thp_split_walk_pmd_entry,
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};
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static inline void thp_split_mm(struct mm_struct *mm)
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{
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#ifdef CONFIG_TRANSPARENT_HUGEPAGE
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struct vm_area_struct *vma;
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unsigned long addr;
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for (vma = mm->mmap; vma != NULL; vma = vma->vm_next) {
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for (addr = vma->vm_start;
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addr < vma->vm_end;
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addr += PAGE_SIZE)
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follow_page(vma, addr, FOLL_SPLIT);
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vma->vm_flags &= ~VM_HUGEPAGE;
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vma->vm_flags |= VM_NOHUGEPAGE;
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walk_page_vma(vma, &thp_split_walk_ops, NULL);
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}
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mm->def_flags |= VM_NOHUGEPAGE;
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#endif
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}
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#else
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static inline void thp_split_mm(struct mm_struct *mm)
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{
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}
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#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
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/*
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* Remove all empty zero pages from the mapping for lazy refaulting
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