Re: Selective swap out of processes

["Javier Cabezas Rodríguez" <jcabezas@ac.upc.edu>]

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El mié, 29-08-2007 a las 12:37 +1000, Nick Piggin escribió:
> Simplest will be just to set referenced to 0 right after calling
> page_referenced, in the case you want to forcefully swap out the
> page.
> 
> try_to_unmap will get called later in the same function.

I have tried this solution, but 0 pages are freed...

- RO/EXEC pages mapped from the executable are now skipped due to this
check:

if (!mapping || !remove_mapping(mapping, page))
	goto keep_locked;

The offender is this check in remove_mapping:

if (unlikely(page_count(page) != 2))
	goto cannot_free;

- RW pages mapped from the executable are skipped because pageout
returns PAGE_KEEP.

- Other pages are skipped because try_to_unmap returns SWAP_FAIL.


I also added a call ptep_clear_flush_young for each pte, to satisfy this
check in try_to_unmap_one:

if (!migration && ((vma->vm_flags & VM_LOCKED) ||
      (ptep_clear_flush_young(vma, address, pte)))) {
	ret = SWAP_FAIL;
	goto out_unmap;
}

My code calls the following function for each VMA of the process.  Are
there errors in the function?:

int my_free_pages(struct vm_area_struct * vma, struct mm_struct * mm)
{
	LIST_HEAD(page_list);
	unsigned long nr_taken;
	struct zone * zone = NULL;
	int ret;
	pte_t *pte_k;
	pud_t *pud;
	pmd_t *pmd;
	unsigned long addr;
	struct page * p;
	struct scan_control sc;

	sc.gfp_mask = __GFP_FS;
	sc.may_swap = 1;
	sc.may_writepage = 1;

	for (addr = vma->vm_start, nr_taken = 0; addr < vma->vm_end; addr +=
PAGE_SIZE, nr_taken++) {
		pgd_t *pgd = pgd_offset(mm, addr);
		if (pgd_none(*pgd))
			return;
		pud = pud_offset(pgd, addr);
		if (pud_none(*pud))
			return;
		pmd = pmd_offset(pud, addr);
		if (pmd_none(*pmd))
			return;
		if (pmd_large(*pmd))
			pte_k = (pte_t *)pmd;
		else
			pte_k = pte_offset_kernel(pmd, addr);

		if (pte_k && pte_present(*pte_k)) {
			p = pte_page(*pte_k);
			if (!zone)
				zone = page_zone(p);

			ptep_clear_flush_young(vma, addr, pte_k);
			del_page_from_lru(zone, p);
			list_add(&p->lru, &page_list);
		}
	}

	spin_lock_irq(&zone->lru_lock);
	__mod_zone_page_state(zone, NR_INACTIVE, -nr_taken);
	zone->pages_scanned += nr_taken;
	spin_unlock_irq(&zone->lru_lock);
}


Thanks


Javi

-- 
Javier Cabezas Rodríguez
Phd. Student - DAC (UPC)
jcabezas@ac.upc.edu

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