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tmpfs: radix_tree_preloading 

Nick has observed that shmem.c still uses GFP_ATOMIC when adding to page cache
or swap cache, without any radix tree preload: so tending to deplete emergency
reserves of memory.

GFP_ATOMIC remains appropriate in shmem_writepage's add_to_swap_cache: it's
being called under memory pressure, so must not wait for more memory to become
available.  But shmem_unuse_inode now has a window in which it can and should
preload with GFP_KERNEL, and say GFP_NOWAIT instead of GFP_ATOMIC in its
add_to_page_cache.

shmem_getpage is not so straightforward: its filepage/swappage integrity
relies upon exchanging between caches under spinlock, and it would need a lot
of restructuring to place the preloads correctly.  Instead, follow its pattern
of retrying on races: use GFP_NOWAIT instead of GFP_ATOMIC in
add_to_page_cache, and begin each circuit of the repeat loop with a sleeping
radix_tree_preload, followed immediately by radix_tree_preload_end - that
won't guarantee success in the next add_to_page_cache, but doesn't need to.

And we can then remove that bothersome congestion_wait: when needed, it'll
automatically get done in the course of the radix_tree_preload.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Looks-good-to: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Hugh Dickins 2008-02-04 22:28:54 -08:00 committed by Linus Torvalds
parent 2e0e26c76a
commit b409f9fcf0
1 changed files with 18 additions and 7 deletions
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25
mm/shmem.c
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@ -901,12 +901,16 @@ static int shmem_unuse_inode(struct shmem_inode_info *info, swp_entry_t entry, s
error = 1;
if (!inode)
goto out;
error = radix_tree_preload(GFP_KERNEL);
if (error)
goto out;
error = 1;
spin_lock(&info->lock);
ptr = shmem_swp_entry(info, idx, NULL);
if (ptr && ptr->val == entry.val)
error = add_to_page_cache(page, inode->i_mapping,
idx, GFP_ATOMIC);
idx, GFP_NOWAIT);
if (error == -EEXIST) {
struct page *filepage = find_get_page(inode->i_mapping, idx);
error = 1;
@ -931,6 +935,7 @@ static int shmem_unuse_inode(struct shmem_inode_info *info, swp_entry_t entry, s
if (ptr)
shmem_swp_unmap(ptr);
spin_unlock(&info->lock);
radix_tree_preload_end();
out:
unlock_page(page);
page_cache_release(page);
@ -1185,6 +1190,16 @@ static int shmem_getpage(struct inode *inode, unsigned long idx,
goto done;
error = 0;
gfp = mapping_gfp_mask(mapping);
if (!filepage) {
/*
* Try to preload while we can wait, to not make a habit of
* draining atomic reserves; but don't latch on to this cpu.
*/
error = radix_tree_preload(gfp & ~__GFP_HIGHMEM);
if (error)
goto failed;
radix_tree_preload_end();
}
spin_lock(&info->lock);
shmem_recalc_inode(inode);
@ -1266,7 +1281,7 @@ static int shmem_getpage(struct inode *inode, unsigned long idx,
set_page_dirty(filepage);
swap_free(swap);
} else if (!(error = add_to_page_cache(
swappage, mapping, idx, GFP_ATOMIC))) {
swappage, mapping, idx, GFP_NOWAIT))) {
info->flags |= SHMEM_PAGEIN;
shmem_swp_set(info, entry, 0);
shmem_swp_unmap(entry);
@ -1280,10 +1295,6 @@ static int shmem_getpage(struct inode *inode, unsigned long idx,
spin_unlock(&info->lock);
unlock_page(swappage);
page_cache_release(swappage);
if (error == -ENOMEM) {
/* let kswapd refresh zone for GFP_ATOMICs */
congestion_wait(WRITE, HZ/50);
}
goto repeat;
}
} else if (sgp == SGP_READ && !filepage) {
@ -1338,7 +1349,7 @@ static int shmem_getpage(struct inode *inode, unsigned long idx,
shmem_swp_unmap(entry);
}
if (error || swap.val || 0 != add_to_page_cache_lru(
filepage, mapping, idx, GFP_ATOMIC)) {
filepage, mapping, idx, GFP_NOWAIT)) {
spin_unlock(&info->lock);
page_cache_release(filepage);
shmem_unacct_blocks(info->flags, 1);