linux-kernel - Re: [PATCH v3 17/25] mm: Add __page_cache_alloc

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Message-ID: <20200607030847.GS19604@bombadil.infradead.org>
Date:   Sat, 6 Jun 2020 20:08:47 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Yang Shi <shy828301@...il.com>
Cc:     Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH v3 17/25] mm: Add __page_cache_alloc_order

On Wed, May 06, 2020 at 11:03:06AM -0700, Yang Shi wrote:
> > diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> > index 55199cb5bd66..1169e2428dd7 100644
> > --- a/include/linux/pagemap.h
> > +++ b/include/linux/pagemap.h
> > @@ -205,15 +205,33 @@ static inline int page_cache_add_speculative(struct page *page, int count)
> >         return __page_cache_add_speculative(page, count);
> >  }
> >
> > +static inline gfp_t thp_gfpmask(gfp_t gfp)
> > +{
> > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> > +       /* We'd rather allocate smaller pages than stall a page fault */
> > +       gfp |= GFP_TRANSHUGE_LIGHT;
> 
> This looks not correct. GFP_TRANSHUGE_LIGHT may set GFP_FS, but some
> filesystem may expect GFP_NOFS, i.e. in readahead path.

Apologies, I overlooked this mail.

In one of the prerequisite patches for this patch set (which is now merged
as f2c817bed58d9be2051fad1d18e167e173c0c227), we call memalloc_nofs_save()
in the readahead path.  That ensures all allocations will have GFP_NOFS
set by the time the page allocator sees them.

Thanks for checking on this.