page cache

Linux 6.18.37 LTS: mm/filemap.c
Linux 6.18.37 LTS: mm/readahead.c
Linux 6.18.37 LTS: mm/page-writeback.c
Linux 6.18.37 LTS: include/linux/pagemap.h

		xas_reset(&xas);
	}
	rcu_read_unlock();
}

static int filemap_read_folio(struct file *file, filler_t filler,
		struct folio *folio)
{
	bool workingset = folio_test_workingset(folio);
	unsigned long pflags;
	int error;

	/*
	 * A previous I/O error may have been due to temporary failures,
	 * eg. multipath errors.  PG_error will be set again if read_folio
	 * fails.
	 */
	folio_clear_error(folio);

	/* Start the actual read. The read will unlock the page. */
	if (unlikely(workingset))
		psi_memstall_enter(&pflags);
	error = filler(file, folio);
	if (unlikely(workingset))
		psi_memstall_leave(&pflags);
	if (error)
		return error;

	error = folio_wait_locked_killable(folio);
	if (error)
		return error;
	if (folio_test_uptodate(folio))
		return 0;
	if (file)
		shrink_readahead_size_eio(&file->f_ra);
	return -EIO;
}

static bool filemap_range_uptodate(struct address_space *mapping,
		loff_t pos, size_t count, struct folio *folio,

		free_folio(old);
	folio_put(old);
}
EXPORT_SYMBOL_GPL(replace_page_cache_folio);

noinline int __filemap_add_folio(struct address_space *mapping,
		struct folio *folio, pgoff_t index, gfp_t gfp, void **shadowp)
{
	XA_STATE(xas, &mapping->i_pages, index);
	int huge = folio_test_hugetlb(folio);
	bool charged = false;
	long nr = 1;

	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
	VM_BUG_ON_FOLIO(folio_test_swapbacked(folio), folio);
	mapping_set_update(&xas, mapping);

	if (!huge) {
		int error = mem_cgroup_charge(folio, NULL, gfp);
		VM_BUG_ON_FOLIO(index & (folio_nr_pages(folio) - 1), folio);
		if (error)
			return error;
		charged = true;
		xas_set_order(&xas, index, folio_order(folio));
		nr = folio_nr_pages(folio);
	}

	gfp &= GFP_RECLAIM_MASK;
	folio_ref_add(folio, nr);
	folio->mapping = mapping;
	folio->index = xas.xa_index;

	do {
		unsigned int order = xa_get_order(xas.xa, xas.xa_index);
		void *entry, *old = NULL;

		if (order > folio_order(folio))
			xas_split_alloc(&xas, xa_load(xas.xa, xas.xa_index),
					order, gfp);
		xas_lock_irq(&xas);