linux-kernel - Re: [PATCH v7 5/6] mm,thp: add read-only THP support for (non-shmem) FS

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Date:   Mon, 24 Jun 2019 17:27:47 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Song Liu <songliubraving@...com>
Cc:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "matthew.wilcox@...cle.com" <matthew.wilcox@...cle.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        Kernel Team <Kernel-team@...com>,
        "william.kucharski@...cle.com" <william.kucharski@...cle.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "hdanton@...a.com" <hdanton@...a.com>
Subject: Re: [PATCH v7 5/6] mm,thp: add read-only THP support for (non-shmem)
 FS

On Mon, Jun 24, 2019 at 02:01:05PM +0000, Song Liu wrote:
> >> @@ -1392,6 +1403,23 @@ static void collapse_file(struct mm_struct *mm,
> >> 				result = SCAN_FAIL;
> >> 				goto xa_unlocked;
> >> 			}
> >> +		} else if (!page || xa_is_value(page)) {
> >> +			xas_unlock_irq(&xas);
> >> +			page_cache_sync_readahead(mapping, &file->f_ra, file,
> >> +						  index, PAGE_SIZE);
> >> +			lru_add_drain();
> > 
> > Why?
> 
> isolate_lru_page() is likely to fail if we don't drain the pagevecs. 

Please add a comment.

> >> +			page = find_lock_page(mapping, index);
> >> +			if (unlikely(page == NULL)) {
> >> +				result = SCAN_FAIL;
> >> +				goto xa_unlocked;
> >> +			}
> >> +		} else if (!PageUptodate(page)) {
> > 
> > Maybe we should try wait_on_page_locked() here before give up?
> 
> Are you referring to the "if (!PageUptodate(page))" case? 

Yes.

-- 
 Kirill A. Shutemov