> On Fri, Mar 7, 2025 at 12:26 AM Christoph Hellwig <hch@xxxxxxxxxxxxx> > wrote: > > > > On Thu, Mar 06, 2025 at 04:40:56PM +0900, Sooyong Suk wrote: > > > There are GUP references to pages that are serving as direct IO > buffers. > > > Those pages can be allocated from CMA pageblocks despite they can be > > > pinned until the DIO is completed. > > > > direct I/O is eactly the case that is not FOLL_LONGTERM and one of the > > reasons to even have the flag. So big fat no to this. > > > Understood. > Hello, thank you for your comment. > We, Sooyong and I, wanted to get some opinions about this FOLL_LONGTERM > for direct I/O as CMA memory got pinned pages which had been pinned from > direct io. > > > You also completely failed to address the relevant mailinglist and > > maintainers. > > I added block maintainer Jens Axboe and the block layer maillinst here, > and added Suren and Sandeep, too. Then, what do you think of using PF_MEMALLOC_PIN for this context as below? This will only remove __GFP_MOVABLE from its allocation flag. Since __bio_iov_iter_get_pages() indicates that it will pin user or kernel pages, there seems to be no reason not to use this process flag. block/bio.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/block/bio.c b/block/bio.c index 65c796ecb..671e28966 100644 --- a/block/bio.c +++ b/block/bio.c @@ -1248,6 +1248,7 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter) unsigned len, i = 0; size_t offset; int ret = 0; + unsigned int flags; /* * Move page array up in the allocated memory for the bio vecs as far as @@ -1267,9 +1268,11 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter) * result to ensure the bio's total size is correct. The remainder of * the iov data will be picked up in the next bio iteration. */ + flags = memalloc_pin_save(); size = iov_iter_extract_pages(iter, &pages, UINT_MAX - bio->bi_iter.bi_size, nr_pages, extraction_flags, &offset); + memalloc_pin_restore(flags); if (unlikely(size <= 0)) return size ? size : -EFAULT;
